The invention discloses an automatic vertical butt joint/decomposition system for large cabin section of spacecraft. The system mainly comprises a support module, a lifting bracket, a position postureadjusting mechanism and a monitoring module. The position and attitude of the communication cabin and the satellite platform can be fed back through the monitoring module, and the position and posture of the satellite platform can be adjusted correspondingly so as to realize the quantification of the relative position between the assembly parts and the quantification of the final positioning precision, thereby realizing accurate control of butt joint and decomposition. The system can greatly improve the butt joint and the decomposition efficiency of the large cabin section, effectively simplify the butt joint and the decomposition process, and ensure the assembly implementation reliability.