Taking a certain type of low voltage distribution box as the research object, the velocity and temperature field in the low voltage distribution box under ambient temperature are calculated by the method of numerical heat transfer. The temperature distributions of circuit breaker, copper bar and cabinet surface in marine distribution box are studied in detail. The special points in the distribution box are tested, and the test results are basically consistent with the evaluation set.The results of calculation and test show that the design of distribution cabinet is reasonable. The temperature rise of the important parts in the distribution box meets the requirement of the code GJB202A. The methods and conclusions of research have reference value for improving the heat dissipation effect of distribution box.