The invention relates to a diesel and natural gas dual-fuel engine starting and jetting system and a control method. A compressed air supply system and a natural gas supply system are respectively connected into a main gas supply pipe through a compressed air control valve and a gas supply control valve. Jetting valves of cylinders are respectively connected with a main gas supply pipe and a main air supply pipe through respective branch gas supply pipes and branch air supply pipes, and an ECU (electronic control unit) controls the natural gas supply control valve, the air supply control valve and the jetting valves of cylinder heads in opening and closing. During starting, the compressed air supply control valve is switched off and the natural gas supply control valve is switched on, so that the natural gas supply system is communicated with the main natural gas supply pipe. The jetting valves on the cylinders inject natural gas into the cylinders when in suction stroke of the cylinders. The diesel and natural gas dual-fuel engine starting and jetting system in one structure is provided with two functions and is controlled electronically. Affection on air injection from supply of natural gas is eliminated, control degree of burning is improved, dual-fuel working process in the cylinders is completed, and maintenance cost is saved.