A system for a deep-sea planktonic microorganism in-situ concentration, temperature maintaining and pressure maintaining sampling is provided and includes a sampling cylinder body with double layer structures, the sampling cylinder body is provided with a plug-shaped inner cavity, the plug-shaped inner cavity is provided with a transfer water outlet and a water inlet connected to a water inlet component, the plug-shaped inner cavity is connected to an end cover, the plug-shaped inner cavity is connected to a filter part, the sampling cylinder body is provided with a sampling water outlet, the sampling water outlet is respectively connected to a pressure maintaining device and a water outlet pipe, a temperature maintaining material layer and a temperature control component are connected between the double layer structures, and the temperature control component is electrically connected to a controller. The system can complete sampling on the premise of maintaining in-situ pressure of samples.