Motor train unit feces collecting system and operating method thereof

A motor train unit feces collecting system and an operating method thereof solve the problems of high energy consumption and complicated structure. A reciprocating motion device directly drives a piston to alternately change the positive and negative pressure in sewage disposal, without providing an intermediate tank, so the system is simple in structure and low in energy consumption. The system includes a blow-off line for connecting a toilet with a sewage tank and connected to a positive and negative pressure switching device which includes a by-pass line, the openings at both ends of the by-pass line are in communication with the blow-off line, a piston is disposed in the by-pass line and connected to a reciprocating motion device which drives the piston to move to change the positive and negative pressure condition of upper and lower regions of the by-pass line.