A system to diagnose a malfunction of a torque sensor in a vehicle steering system includes a voltage difference generator that outputs a voltage difference by comparing a voltage of a contact part between a temperature correcting coil and a torque detecting coil in a torque sensor for a steering system and an offset voltage generated from an offset voltage generator, a malfunction determining part that determines a malfunction by comparing a reference voltage and an output voltage of said voltage difference generator, and a controller that executes a neutral steering when a malfunction is determined in said malfunction determining part.