Abstract: In order to carry out power transient tests for PWR fuel element in China Advanced Research Reactor (CARR), the research and conceptual design of 3He pressure control loop were completed. The working principle, design parameters and technological flow of the loop were described. It is seen that the 3He loop can adjust the power of the tested PWR fuel element rapidly, evenly and flexibly and it is an optimal path to realize the power transient regulation for tested PWR fuel.