Self-circulating evaporative cooling technology makes use of the latent heat of working medium phase change to meet high heat flux requirement during the operation of flexible HVDC converter valve. In this paper, a one-dimensional simulation model is established to solve the problem of multi-branch parallel heat source with strong non-uniform heat flux, and a multi-branch self-circulating evaporative cooling experimental system is designed. The accuracy of this model is verified to be better than 9.3%. The model analysis shows that under non-uniform heat flux, the temperature distribution equilibrium is 4.78 in inverter condition and 3.52 in rectifier condition. With the increase of operating pressure, the equilibrium of temperature distribution on the outer wall of the liquid tank is improved. Considering the complexity and cost of this cooling system, single condenser is recommend as the system configuration.