A variable valve lift system for an internal combustion engine includes a roller rocker lift mechanism and a driving mechanism. A cam and a roller of the roller rocker lift mechanism cooperate with each other to control valve lift. The roller rocker lift mechanism includes a second rocker arm, wherein one end of the second rocker arm is connected with the driving mechanism by a rotation pin so as to create a straight-line displacement of the driving mechanism; the second rocker arm is provided with a guideway in the direction of the straight-line displacement; a rocker-arm pin of the roller rocker lift mechanism is slidably set in the guideway of the second rocker. According to actual work condition of the internal combustion engine, the valve lift is regulated by a motor; and continuous variable valve lift is provided from low speed to high speed.