Obstacle-crossing capability is an important index to evaluate the performance of power transmission line inspection robots. Based on the quasi-static analysis，it compared the obstacle-crossing process of the inspection robot with large-diameter wheels and the inspection robot with passive joints，and calculated the maximum height that the robots can cross and the power consuming during the obstacle-crossing. The comparison results indicate that the inspection robot with passive joints has a better obstacle -crossing performance and power consuming requirement，which means the design of passive joints promotes the safety and stability during obstacle-crossing. The obstacle-crossing performance of the inspection robot with passive joints has been demonstrated by both simulation and field experiment. The research provides the theoretic reference for the inspection robot scheme and mechanical design.