For the composite component assembly interference problem caused by molding errors， this paper proposed a method of dimensional reduction of composite component assembly interference and clearance based on point cloud data obtained from laser equipment， it converts the interference and clearance calculation of the three-dimensional assembly into the calculation of the two-dimensional boundary distance. Taking a certain type of aircraft random assembly as an example，the feasibility of the proposed method and algorithm is verified through experiments， and the assembly accuracy and efficiency are improved compared with the original assembly process.