Abstract: The mechanical properties of bottom hole assembly (BHA) directly affect wellbore quality,drilling speed and safety,thus it is necessary to study the mechanical properties of BHA based on theories and experiments.However,the experimental study is inadequate so far.According to the similarity theory,the bottom drill string mechanics device is used to simulate the effect of weight on bit (WOB) and rotary speed on inclinational force,azimuthal force,total side forces and directional angle.The results indicate that total side forces at bit increases with the increase of WOB,but the rotary speed affects it slightly;the inclination force increases with the increase of WOB,and the higher the rotary speed;the greater the inclination force,too,azimuthal force increases with the increase of WOB,and rotary speed affects it slightly;the direction angle caused by total side forces decreases with the increase of WOB,and increases with the increase of rotary speed.It can provide basis for the study on mechanism of well deviation control and fast drilling.