The invention discloses a low-pressure gas supercharged engine running mode switching device. The device comprises an inlet manifold and an exhaust pipe which are mounted on an engine body, the inletmanifold is connected with an air inlet pipe, an air filter, a pressurizer, an intercooler and an electronic throttle valve, the air filter, the pressurizer, the intercooler and the electronic throttle valve are mounted in sequence, a low-pressure gas pipe is further included, a starting mode gas conveying device and a work mode gas conveying device are in parallel connection to the low-pressure gas pipe, the electronic throttle valve, the starting mode gas conveying device and the work mode gas conveying device are connected with a running mode switching control device, and the invention further discloses a switching control method of the device. Under the starting running mode, mixed gas does not pass through the pressurizer and the intercooler, the advancing length of the mixed gas is shortened, the starting time of an engine is greatly shortened, and the starting property is improved. After the engine enters in the work running mode, engine intake can be pressurized, the device issuitable for high-power running, engine self suction and pressurizing mixed use can be achieved, and the running property of the engine is improved.