Ha Long Bay and Cat Ba have well developed coral reefs in the past, this is the habitat of thousands of marine species, including high economic value and endangered species. In the study shows that coral reefs in Ha Long and Cat Ba areas have completely changed when compared to the results of previous studies because of environmental pollution. Coral reefs have changed on structure, profile and spatial distribution. The number of coral species decreased significantly (lost about 1/3), there haven't got any reefs in excellent and very good reef (over 50 percent living coral cover), only few reefs are good reef (30-50 percent), almost reefs are fair and poor reefs (0-30 percent). Vertical distribution of corals is reduced (.6 meters, common 2-4m). Living organisms on the reef is also reduceq due to habitat loss. Although both areas are strictly management, but environmental issues have not been improved so that the reefs here are still In decline and no signs of restoration, substrate is no longer suitable for recruitment of coral larvae. Disease, predator, marine culture and tourism are outbreak in the area, therefore coral reefs is more and more reduced.