Trailer pneumatic braking system and parking braking method thereof

The invention provides a trailer pneumatic braking system and a parking braking method thereof. The trailer pneumatic braking system comprises three trailer gas circuit connectors, a four-circuit protection valve, a trailer emergency relay valve, two traveling relay valves, three gas cylinders and a parking relay valve. A three-pipeline gas circuit connector (a red trailer handle, a yellow trailerhandle and a white trailer handle) is adopted, and under the simultaneous action of the four-circuit protection valve and the trailer emergency relay valve, a double-loop travelling brake system guarantees that normal work of the other circuit is not affected when one circuit fails. The parking brake loop enables a trailer and a brake air chamber spring cavity of a tractor to achieve synchronousaction, and in-situ spring parking after uncoupling is achieved. The system can be matched with the tractor with the trailer gas circuit connector of three pipelines (red, yellow and white handles), can also be matched with th