It is difficult to be placed in the position of the laser tracker to meet the requirement of measuring accuracy for the special environment such as the external disassembly and reassembly of a certain type of fork type wing-fuselage docking aircraft. Firstly, this paper presents a direct measurement method based on vision. Secondly, builds the measurement system model, analyzes the key technology of vision measurement system involved, and presents a method of ellipse detection based on arc combination. Finally, through the simulation test of fork type wing-fuselagedocking, verifies the actual feasibility of these method. The experimental results show that the cross axis gap distance measurement precision can reach 0.03mm, and the axis angle measurement accuracy reaches 0.025°, which meets the requirements of actual docking measurement.