The utility model relates to a single-stage double-acting hydraulic cylinder. The single-stage double-acting hydraulic cylinder comprises pistons, a cylinder barrel, valve seats, a piston rod, a guide block and a long pull rod, wherein the cylinder barrel comprises an upper cylinder barrel and a lower cylinder barrel, the upper cylinder barrel and the lower cylinder barrel are connected by the guide block, the piston rod penetrates through the guide block vertically, the upper end of the piston rod is arranged in the upper cylinder barrel, the lower end of the piston rod is arranged in the lower cylinder barrel, the pistons are arranged at two ends of the piston rod, an upper valve seat is arranged at the upper end of the upper cylinder barrel, a lower valve seat is arranged at the lower end of the lower cylinder barrel, and a gas inlet and a gas exhaust port are formed on each of the upper valve seat and the lower valve seat. The single-stage double-acting hydraulic cylinder has the advantages of simple structure, large gas displacement and high compression efficiency, and is especially suitable for a booster compressor with small compression ratio and large gas displacement.