The application provides a synchronous telescopic mechanism for a truck-mounted crane, which includes a basic arm, a first telescopic arm, a second telescopic arm, and a third telescopic arm that are sequentially socketed in the basic arm, a multi-stage telescopic oil cylinder and a rope row mechanism , the rope row mechanism includes a first boom rope assembly, a second boom rope assembly, a first retractable boom rope assembly and a second retractable boom rope assembly, and the multi-stage telescopic oil cylinder includes a piston rod, a primary cylinder, The secondary cylinder and the bracket arranged at the end of the secondary cylinder away from the primary cylinder, the first outrigger rope assembly includes a first outrigger wheel and a first outrigger rope, and the second outrigger The boom rope assembly includes a second boom rope assembly and a second boom rope assembly, the first boom rope assembly includes a first boom rope assembly and a first boom rope assembly, and the second boom rope assembly includes a second boom rope assembly wheel and the second retractable arm rope, the synchronous telescopic mechanism has the characteristics of simple structure and convenient installation.