The invention discloses a road intersection traffic light control system and a control method thereof. Vehicle delay minimizing is not the only purpose, and the optimization objective is that the traffic safety of a pedestrian who crosses a road forcibly is guaranteed. Due to the fact that when an initial green light is over, the fact whether the pedestrian who is in conflict with the current phase condition crosses the road forcibly is judged, whether the duration time of the green light is prolonged is determined. When the initial green light is over, if the pedestrian who is in conflict with the current phase condition crosses the road forcibly, the duration time of the green light is prolonged, otherwise, the phase condition of the green light and a red light is changed normally. Due to the fact that ultimate prolonging time is set, not only is the safety of the pedestrian who crosses the road forcibly guaranteed, but also the delay at a road intersection is avoided. Therefore, the possibility that when the pedestrian crosses the road forcibly, accidents happen is reduced, the person oriented idea is emphasized, and the control system and the control method are particularly suitable for traffic control on a city intersection of a low-saturation city.