The coral reef ecosystem plays an important role in scientific research and economy. An assessment research on status of the coral reefs was carried out at 6 sites of coastal water from Nghi Son (Thanh Hoa province) to Vung Ro (Khanh Hoa province), Viet Nam between October and December 2015. The research was done using the manta tow method for rapid reef assessment and reef area determination, using reef check for detailed assessment of reef substrate types, etc. 288 species of hard corals under 57 genera and 14 families were identified from the study sites. These species mainly belonged to 4 families, namely Acroporidae, Faviidae, Poritidae and Fungiidae. The research showed the bad condition of the reef at all study sites through such indicators as a low live hard coral cover (average cover of 19.8%), high dead coral cover, recently killed coral, fleshy seaweed, etc. Most of surveyed transects had poor level of hard coral cover, the number of transects having good coral cover was unsignificant. The total reef area of 6 surveyed sites was 809.5 hectares, mainly occupied in Son Tra and Vung Ro. This was the first time coral disease and bleaching widely ranged had been observed and described. However, the reason of this phenomenon has not been mentioned yet and there is a need for more detailed researches on these problems in the coming time to have a basis for protection and management of coral reef ecosystem in Vietnam's coastal water.