The invention relates to a ring main unit (RMU) anti-condensation tester, which is provided with a box body and a condensate plate located in a RMU. An air inlet is disposed on the top of the box body. A condensation collection chamber is disposed in the box body. The air inlet is connected to the upper opening of the condensation collection chamber. One side of the condensation collection chamberis connected to a condenser. The lower part of the condensation collection chamber is provided with a drainage port. The drainage port is connected to a drain pipe. A water outlet is disposed on thebottom of the box body. A water tank is disposed outside the box body. The drain pipe is connected to the water tank through the water outlet. An ultrasonic atomizer is disposed inside the box body. Apower supply and a controller are disposed inside the box body. The ultrasonic atomizer and the condenser are connected to a controller. The condensate plate is located under the top cover of the RMU. A thermoelectric cooler is arranged on the condensate plate. The cold-end working surface of the thermoelectric cooler is located on the upper surface of the condensate plate. The hot-end working surface of the thermoelectric cooler is located on the lower surface of the condensate plate. The upper end of the condensate plate is provided with a vent hole. The RMU anti-condensation tester can atomize and collect the condensation and monitor the humidity in real time.