Belonging to deep-sea biotechnologies, the invention aims to provide a sampler for deep-sea microorganism pressure-maintaining transfer. The sample comprises a gravity piston type sampling mechanism, a fixed ball valve mechanism and a travel switch ball valve mechanism. The gravity piston type sampling mechanism consists of a heavy hammer mechanism, a hoisting mechanism, a truth-preserving sampling cylinder and an energy accumulator. The heavy hammer mechanism includes a heavy hammer, a heavy hammer cable and a lever, wherein the heavy hammer is suspended at one end of the heavy hammer cable through lifting screws, the other end of the heavy hammer cable is suspended at the other end of the lever through a shackle, and the other end of the lever is fixed on a main steel cable through a clamp plate. The hoisting mechanism comprises a release cable, a guiding device, a piston and a travel switch ball valve suspension cable. According to the invention, the travel switch ball valve is designed to realize sealing of a sample at the lower end of the truth-preserving cylinder, the upper end of the sample still adopts piston sealing, and the travel switch ball valve utilizes the axial relative movement of itself and the truth-preserving cylinder to realize open-close of the ball valve.