The invention discloses a telescopic guide rail protection cover reliability testing stand and solves a problem that a fault of a numerical control machine tool guide rail protection cover in the prior art is difficult to detect. The testing stand comprises a state monitoring alarm mechanism, an automatic speed change control mechanism, a protection cover telescoping mechanism and an environment test system, wherein the environment test system comprises a simulation main shaft support, a second motor, a rotary body, a cutting fluid oil tank and an oil return groove, the protection cover telescoping mechanism is mounted on the ground base through a work stand, the simulation main shaft support is mounted in front of a right side of the work stand, the second motor is mounted on a top board of the simulation main shaft support, the second motor is connected with the rotary body, the cutting fluid oil tank is mounted at a right side of the simulation main shaft support, the cutting fluid oil tank is connected with a rotary body pipeline, the oil return groove is mounted at periphery of the work stand, the cutting fluid oil tank is connected with an oil return groove pipeline, the automatic speed change control mechanism is mounted at a right side of the work stand, a frequency converter is connected with the second motor and a first motor, a humidity sensor of the state monitoring alarm mechanism is mounted on the work stand, and the humidity sensor is connected with a host industrial control computer.