Abstract: Different designs of ~³He gas screen structure are modeled and analyzed with MCNP code along with the PRT（Power Ramp Test） device installed in a HFETR core. Based on the neutronics computation results, the designs are evaluated quantitatively with a multi-objective evaluation method. The results show that when the location of the ~³He gas screen is fixed, the design with a thicker ~³He gas layer has a lower fuel rod power. Variation range of the test fuel rod power is acceptable when the ~³He gas screen has a ~³He gas layer with the thickness as 2 to 5 mm. When the distance from the fuel rod to the ~³He gas screen with a 3 mm thick gas layer is larger, the ~³He gas screen has less control of the test fuel rod power for a higher thermal neutron flux level in the rod and a larger reactivity addition during the test. Based on the marks by a quantitatively evaluation method, the optimal design of ~³He gas screen structure with a 3 mm thick ~³He gas layer and 2 mm thick annual inner flow channel, is identified for a PRT device and a typical HFETR core arrangement.