An actuator of a medical device, comprising: a housing; a driving unit mounted in the housing; a first moving unit mounted in the housing and being capable of sliding relative to the housing under the driving of the driving unit, the first moving unit comprising a movable first car; a spring with two ends thereof abutting the housing and first car, respectively; and a first lock formed between the driving unit and first car, the first lock comprising a first snap and a first protrusion being detachably engagable in the first snap, one of the first snap and first protrusion being formed on the first car, and the other one of the first snap and first protrusion being formed on the driving unit; a second moving unit being capable of sliding relative to housing, the seconding moving unit comprising a movable second car, a second lock formed between the first and second cars, the second lock comprising a second protrusion formed on one of the first and second cars, and a second snap formed on the other one of the first and second cars, the second protrusion being detachably engagable in the second snap, characterized in that when the second protrusion is engaged with the second snap, the first and second cars (32, 52) are connected together and spaced from each other by a predetermined distance such that when the first protrusion disengages from the first snap, the spring moves the first car and the second car in tandem relative to the housing; and when the second protrusion is also disengaged from the second snap, the first car further slides relative to the second car under a restoring force of the spring. a housing; a driving unit mounted in the housing; a first moving unit mounted in the housing and being capable of sliding relative to the housing under the driving of the driving unit, the first moving unit comprising a movable first car; a spring with two ends thereof abutting the housing and first car, respectively; and a first lock formed between the driving unit and first car, the first lock comprising a first snap and a first protrusion being detachably engagable in the first snap, one of the first snap and first protrusion being formed on the first car, and the other one of the first snap and first protrusion being formed on the driving unit; a second moving unit being capable of sliding relative to housing, the seconding moving unit comprising a movable second car, a second lock formed between the first and second cars, the second lock comprising a second protrusion formed on one of the first and second cars, and a second snap formed on the other one of the first and second cars, the second protrusion being detachably engagable in the second snap, characterized in that when the second protrusion is engaged with the second snap, the first and second cars (32, 52) are connected together and spaced from each other by a predetermined distance such that when the first protrusion disengages from the first snap, the spring moves the first car and the second car in tandem relative to the housing; and when the second protrusion is also disengaged from the second snap, the first car further slides relative to the second car under a restoring force of the spring.