A driving method of an optical actuator is applied to a projection system. The optical actuator includes a carrier, an optical element and an actuator component. The optical element is disposed at the carrier. The actuator component drives the carrier to rotate an angle. The driving method includes the steps of providing a driving signal having an initial section and a target section, and shifting the optical element between a position driven by the initial section and a position driven by the target section via the actuator component according to a first acceleration-deceleration section and a second acceleration-deceleration section. In addition, an optical actuator, a projection lens module and a projection system are also disclosed.