The invention provides a variable cross-section space angle steel component assembling precision control method and system. The method comprises the following steps of detecting a jig frame platform, marking out the jig frame platform, installing the system on the jig frame platform, finely adjusting the system, performing secondary fine adjustment on the system after a steel tower component is in place, assembling segments, disassembling the system and reusing the system. The problems that an existing segment manufacturing method and tool are low in efficiency, large in material consumption, large in damage, low in universality, large in man-machine consumption for disassembly and assembly and potential safety hazards exist are solved. The system is accurate in precision control, wide in application range, high in repeated utilization rate, convenient to operate and good in safety; the method can be used for assembling and precision control of various variable cross-section space angle steel members, the manufacturing precision is guaranteed, meanwhile, the production efficiency is improved by two times, the tool cost is reduced by 50%, and cost reduction and efficiency improvement are remarkable; positioning, assembling and adjusting are convenient and fast; labor and machinery can be saved in each link, and construction tasks can be efficiently completed.