The invention discloses a steel component deformation analysis based virtual pre-assembly error judgment method. The method includes: in a structural design stage, subjecting a structural unit to structural deformation analysis according to a construction scheme and operating conditions, and determining a structural pre-camber value to complete structural design optimization; processing componentsin a factory according to an optimized design scheme; after processing, subjecting the components to scanning detection and virtual preassembly, adopting an optimized calculation model to simulate constraint conditions and influence factors in scanning in design analysis software, calculating deformation delta 1 of scanned components, subjecting deviation delta 2 analyzed by a scanning model andthe deformation analysis delta 1 to result superposition to obtain practical processing deviation delta. By structural deformation analysis, accuracy in steel component virtual preassembly detection is improved, and reliable data guarantee is provided for steel structure virtual preassembly.