Since the current researches about hydrothermal extraction was mainly relying on microwave intensification, which has the problems of small penetration depth and poor heating uniformity, a method of radio frequency (RF) with better heating uniformity was used to heat and a set of hydrothermal reactor suitable for RF intensification was designed based on the horizontal parallel electrodes RF heating system. This hydrothermal reactor was mainly composed of four parts: double-layer autoclave, pressure regulator, fiber-optical thermometer and air-driven magnetic stirrer. Firstly, the overall structure and working principle were explained. Then the key components of the double-layer autoclave and air-driven magnetic stirrer were designed in detail based on the stress analysis theory of the internal pressure thin-wall cylinder and the magnetic coupling transmission theory, and the pressure regulator and fiber-optical thermometer were designed and selected, respectively. Finally, the experimental platform of RF intensify hydrothermal reaction was built and the stirring speed, liquid/solid ratio (LSR) and RF electrode gap were selected to test the stirring and heating performance of the hydrothermal reactor. The results showed that there was no significant difference for the stirring speed between the experimental groups and control group (pure water), when the LSR was greater than 20 mL/g (p>0.05), and the LSR was no longer the main factor affecting the stirring speed. When the LSR was less than 40 mL/g, and the stirring speed was greater than 150 r/min, the electrodes gaps was the main factor affecting the heating rate of sample, and the heating rate was increased continuously with the reduction of the electrodes gaps. When the electrodes gap was 130 mm, the heating rate can reach 8~10℃/min. The development of this reactor can provide important technical support for the experimental research of hydrothermal extraction based on RF intensification.