The invention discloses a telescopic cylinder. The telescopic cylinder comprises a cylinder barrel. A piston is arranged in the cylinder barrel. One end of the cylinder barrel is provided with a first oil inlet. The sidewall of the other end of the cylinder barrel is provided with a second oil inlet. The interior of the piston is hollow. An oil inlet pipe is arranged in the piston. The side face of the piston is provided with a third oil inlet. The tail of the piston is provided with an oil outlet. In the process of stretching and retracting of the cylinder, hydraulic oil goes in through the oil inlet pipe in the piston and the gap between the oil inlet pipe and the piston in sequence to realize two-channel oil taking. The number of oil pipes is reduced. Meanwhile, connectors required by the oil pipes are decreased, the probability of oil leakage is greatly reduced. The stability of oil channels is improved. Through structure simplification, maintenance work is more convenient and faster.