Disclosed is a portable start-up power supply comprising supercapacitors, lithium-ion batteries, a supercapacitor precharge module, a parallel switch module, a battery management system (BMS), a charging module, a controller, a switch and a car battery bridging and protection module, wherein the controller is connected with the charging module, the BMS, the supercapacitor precharge module, the parallel switch module, the supercapacitors, the car battery bridging and protection module, and the switch; the charging module is connected with the lithium-ion batteries through the BMS; the positive electrode of the lithium-ion battery is connected with the positive electrode of the supercapacitor through the supercapacitor precharge module; the supercapacitors is connected with the car battery bridging and protection module; and the parallel switch module is connected with the lithium-ion batteries and the supercapacitors. The lithium-ion batteries in combination with the supercapacitors realize complementary advantages, so that the present invention has an excellent start-up performance even at an extremely low temperature.