A control system for a screen of a vehicle includes a global positioning system (GPS), an inertia sensor and a control circuit. The GPS detects a satellite signal from a satellite. The inertia sensor senses motion of the vehicle and correspondingly generates a motion state value. The control circuit performs one of a first determination procedure and a second determination procedure according to the state of the satellite signal. In the first determination procedure, the control circuit calculates the vehicle speed of the vehicle according to the satellite signal, and selectively locks the screen of the vehicle according to the vehicle speed. In the second determination procedure, the control circuit generates a motion signal according to the motion state value, and selectively locks the screen of the vehicle according to the motion signal. Accordingly, driving safety can still be effectively ensured even in the case of poor satellite signals.