Abstract: After collecting and sorting out the first-hand information of 31 people injured by 2 successive M5.0 earthquakes in Tonghai County, Yunnan province, we analyzed the age, gender, traumatic condition, and the accident spots of the injured people. It is found that most of injured person were from the hardest-hit and densely populated areas, and women and the aged person were vulnerable, and more were suffering from bone fracture and soft tissue injury. We further analyzed the factors such as earthquake magnitude, original time, aftershocks, and population density and found that the superposition of the two earthquakes' damages, the high population density in the affected areas, the original time in the deep night, and people's over reaction to the two earthquakes constituted the main causes of the heavy injury.