Vibration during drilling can cause fatigue failure and damage to the drilling tool. In order to improve the stability of downhole drilling tool， the author designed a drilling tool structure that relies on the planetary gear system to drive contra rotation of two coaxial bits. The strength verification of its core parts such as gears， seals， bearings， proved that the design strength of the structure can meet the normal working conditions. The vibration effect of the structure has been verified by numerical simulation， where the interaction between the drill bit and rock was simplified as harmonic load to perform harmonic response analysis to solve the vibration of the structure. Compared with the conventional drill structure， the result shows the coaxial contra-rotary drilling tool structure can effectively suppress twisting vibration under the same condition.