A full-sea depth multi-point in-situ sampler includes a sampling assembly, a pressure-retaining assembly, a pressure-compensating assembly, and a cleaning assembly. The sampling assembly includes a handle, an extrusion valve, a needle valve core, a two-stage piston, a sampling tube, and a capturing device. The pressure-retaining assembly includes a pressure-retaining cylinder, a locking mechanism, a floating valve core, a support spring, and a drainage device. The pressure-compensating assembly includes a pressure-compensating cylinder, a piston, and an end cap. The cleaning assembly includes a cleaning sleeve, a cleaning cylinder, and multiple trigger mechanisms. A sampling and transfer method based on the sampler is also provided.