Abstract: A cylinder having a piston assembly capable of stopping once when having moved up and down every time including a housing having a cavity, a gear ring fixedly within the cavity of the housing, a main crankshaft fitted within the cavity of the housing and provided with an eccentric recess, a gear meshed with said gear ring, an auxiliary crankshaft including an upper axle and a lower axle, the upper axle being connected with a piston assembly via connecting rod and having a center tangent to a pitch circle of the gear, the lower axle being pivotally connected with the eccentric recess of the main crankshaft, the gear meshed with the gear ring and fixedly mounted on the lower axle of the auxiliary crankshaft and having gear ratio of 2:3 to the gear ring.