Because of the high drilling capacity of the drill configured for small diameter deep hole diamond drilling, with the high rotation rate and drilling efficiency in the hole sections of medium-depth as well as the less, serious bit burning accidents, diamond bit (core barrel) and rocks sintering, are often caused by the changes of working condition or a certain drilling parameter. With the case of serious bit burning accident, the paper analyzes the working conditions in medium-depth hole section of diamond drilling, there serious bit burning accident is easily happen and discusses the key issues of prevention and treatment of the accidents.