The utility model discloses a proportional valve with a failure protector. An increasing proportional valve is provided with a failure protector, namely, an isometric piston is arranged in a valve body of the increasing proportional valve, wherein the side face of a guiding cylindrical surface at one end of the isometric piston is provided with an oil groove and the end face of one end of the isometric piston is provided with a sealing gasket. A failure protective screw plug is arranged in the valve body of the increasing proportional valve, wherein a control spring sleeve at the center of the failure protective screw plug is arranged on the other end of the isometric piston and the other end of the isometric piston and an outer ring of the failure protective screw plug are both provided with a sealing ring. An oil chamber at one end of the isometric piston is communicated with an input port of a rear wheel through a pipeline, an oil chamber at the middle part of the isometric piston is respectively communicated with an output port of the rear wheel and an output port of the increasing proportional valve and an oil chamber at the other end of the isometric piston is respectively communicated with an output port and an input port of the front wheel. The utility model is used for braking a car model of which the pipeline is arranged in an H shape, and can sufficiently enhance the utilization rate of attachment coefficient under the condition that the rear wheel is not locked; meantime, the utility model has the function of single chamber failure protection.