The invention relates to diagnosis system arranged in a control device of a vehicle system for measuring a plurality of variables respectively, in particular to a diagnosis service system for the brake control device of a rail transit vehicle. The diagnosis service system is a distributed network system and comprises diagnosis service modules which are in the same number as braking control modules, each diagnosis service module is arranged in a braking control module, and the diagnosis service modules are communicated with one another through data. Based on the technical scheme, the inventionprovides the diagnosis service system for the brake control device of the rail transit vehicle, which mainly solves the conflict between the finiteness of the software and hardware resource of the brake control device of the rail transit vehicle and the constantly increasing functional requirements on the diagnosis service system of the control device, and at the same time, increases the flexibility of post diagnosis service system upgrade.