The automatic 4-door mounting system is a vision guiding system applicable to automatic vehicle door loading. Based on the principle of structured light 3-D measuring, the system solves the spatial deviation during actual assembly through acquiring the 3D information of the selected points on vehicle body and car doors to be mounted so as to correct robotic track and enable the robot to assemble car doors correctly. According to the demands for automatic 4-door mounting in automotive assembly, this system can realize inline automatic robot installation for adjustment of the 4-doors of BIW. The system could ensure installation consistency and even clearance between car door and car body, and meanwhile test automatically the gap and flushness after assembly, so that it is unnecessary to adjust the clearance in the following workstation. Problems such as abnormal noise and wear when closing doors or poor internal airtight performance caused by large randomness of assembly error and improper mounting position resulted from non-proficiency of assembling personnel.