Warming poses a significant threat to the utility of deep-sea samples. This study developed an active temperature-preserving deep-sea water sampler to use at full ocean depths. The most important component of the sampler is the pressure-adaptive thermoelectric cooler module; laboratory experiments validated its highpressure resistance and waterproof capability under 110 MPa water conditions. The overall structure of the sampler was then designed, and computational fluid dynamics modeled the samples' temperature distribution. The simulation results were consistent with experimental data. Finally, a sampler prototype was constructed and then tested in the Mariana Trench zone at a large depth of up to 6000 m. Preliminary results indicated that it functioned well during sea trials. The developed sampler should help preserve the in situ temperature of deep-sea samples throughout the recovery process and thus improve the sample quality.