The invention relates to a shielding start technology, in particular to an underground folding start method for assorted trolleys after shielding, which is used for solving the problems of large floor area, long period, high cost, adversity to winter start and the like caused by section-by-section placement and split start. The underground folding start method comprises the following steps: mounting No. 1 and No. 2 trolleys, disassembling No. 3 and No. 4 trolleys on the ground, and hanging the No. 3 and No. 4 trolleys on the left and right sides of the No. 1 and No. 2 trolleys respectively; stopping a shield machine after the shield machine tunnels to a state that the trolleys advance in front of a counterforce frame, moving the No. 3 trolley to the back part of the No. 2 trolley, and moving the No. 4 trolley to the left and right sides of the No. 3 trolley; making the shield machine tunnel to another trolley position, moving left and right frames of the No. 4 trolley to the back part of the No. 3 trolley, making the shield machine continue to tunnel to another trolley position, hanging No. 5 and No. 6 trolleys under the ground continuously, and connecting the No. 5 and No. 6 trolleys with the No. 4 trolley. According to the method, complete underground start is realized, the advantages of easiness in operating, small disassembling and assembling frequency and small debugging range are achieved, the influence on start section tunneling is small, and the safety risk of the start section can be avoided effectively.