Abstract: Compared with slide steering tools, rotary steering tools are more advantageous with high rate of penetration (ROP), small drag and torque, strong horizontal displacement extension ability and flexible well trajectory control. After the push-the-bit rotary steering tool is introduced into domestic markets, its application is overall better, but in some areas, it presents the problem of insufficient buildup capacity. In this paper, variable cross-section BHA (bottom hole assembly) mechanical model and well deviation trend angle analysis model for push-the-bit rotary steering tool were established by means of the BHA beam-column method. And based on this, the influential laws of BHA structure parameters, weight on bit (WOB), bit anisotropy and rock drillability on the buildup capacity of the tool were analyzed. It is indicated that the buildup capacity of the tool is affected more by bias force, length and outer diameter of the first span drilling string, outer diameter of the second span drilling string and lateral cutting capacity of drilling bit. Finally, the BHA of push-the-bit rotary steering tool was structurally optimized based on the analysis results. And its application effect in Tazhong area is better.