It is disclosed an actuation mechanism and ultrasonic surgical instrument. The ultrasonic surgical instrument includes an elongated body, a clamping assembly and an actuation mechanism configured to actuate the clamping assembly. The actuation mechanism includes: a handle portion; a first trigger and a second trigger pivotally arranged on the handle portion, respectively; and a driving member configured to actuate the clamping assembly, where the clamping assembly is arranged on a distal portion of the elongated body. The first trigger is engaged with the driving member through a first link, and the second trigger is engaged with the driving member through the first link and a second link. The first trigger is movable independently with respect to the second trigger during a portion of movement of the first trigger.