Abstract: The speed signal is a key signal of the braking system for subway train. Simulation of the speed signal is a fundamental work in the realization of the braking training system and the braking test system for subway train. This paper proposes a simulation scheme of real-time controllable speed sensor output signal according to the requirement of the signal output from the speed sensor in a rack-controlled braking system for subway train and realizes the simulation. STC15 series single-chip microcomputer is used to output high-speed pulse voltage signals which are then converted into 7 mA-14 mA pulse current signals as output signals for simulating the output signals from the speed sensors during the running process of a subway train. The simulation results show that this scheme meets the requirements of simulating output signals from the speed sensors in subway train and can facilitate improving the operability of the braking test system and the braking training system for subway trains.