With the speeding up of regional economic integration process, the socio-economic structure of the border areas between China and Vietnam has changed, and with the deepening of economic cooperation in the greater Mekong sub-region (GMS), shielding effect in the border areas has weakened, cross-border population migration, such as the population movement of intermarriage and business workers, has become more frequent, so that population in the border areas has become more complex, and the population structure is changed, leading to a series of population security problems. This paper makes an analysis on those problems with the macro-scope statistic data from County Governments and the data from qualitative interviews on illegal cross-border intermarriage in border areas of Yunnan and Guangxi. The results show that cross-border intermarriage in the border areas of the two provinces is increasing rapidly, intermarriage circle extends continuously from the border to the hinterland, cross-border marriage extends broader, Parts of the cross-border marriage will soon turn into the hinterland's transnational marriage, Married population gender structure presents serious imbalance, the number of the women from neighboring countries married into China is much more than that of Chinese women married into the neighbors, the couple’s education-cultural quality of the across border marriage is very low, their cultural levels are mostly primary school and junior high school, the couple’s education resources present a combination of weakness and weakness, across border marriage registration rates is very low, mostly in the form of de facto marriage family in China, And early marriage and many births phenomena in those families are serious, that would not be conducive to China family planning implementation. Couples’ age difference is too large and the cross-border marriages have features of intergenerational inheritance. Further analysis finds that the causes leading to the continuous increase of the cross-border marriage are closely related to the geo-spatial proximity of Vietnam, the homology of cross-border cultural circles, the closure of the marriage circles, the promotion of the two-level economic stair among the neighboring countries, China border areas and inland China, the cumbersome marriage registration procedures and high cost, the complementarity between the two countries’ population sex structure, the dislocation of the marriage system between the two countries, and the instability of the political situation in the border areas. It is difficult to effectively connect the marriage institutions of China and Vietnam because of the great difference of marriage systems between the two countries, including marriage registration certificate requirements, the legal age for marriage, marriage registration fees, and so on. To accomplish this, a special marriage registration agency or department in the border areas should be set up to maintain the reasonable pursuit of cross-border marriages of those people. Traditional security development strategies pay attention to the competition processes, obtaining a relative earning, while non-traditional ones lay more emphasis on cooperation to get absolute return. “Cooperation” should not only be embodied at the sector levels, but also at the national and international levels. China and her neighbors should not be a “zero sum game”, but a benign interaction process. In short, the persistence of Yunnan and Guangxi border areas cross-border marriage is not only connected with historical reasons, but also with the reality conditions, not only affected by cross-border ethnicity’s cultural assimilation, but also by the political restrictions and economic role of China and Vietnam, not only restricted by macro social structures, but also related to the micro life custom of the inhabitants living in the border areas. Cross-border marriage of those people from border areas in Yunnan and Guangxi has become a stable mate model, forming a unique marriage culture in the border areas. That is the result of the inter-action among many factors, and needs to be surveyed from long-term strategic view.