Abstract: To optimize the design of tissue-equivalent proportional counter(TEPC) and make it satisfy the measurement of radiation field with high fluence rate, we set up a TEPC based on a Gas Electron Multiplier（GEM）.The effective gain is very important for GEM-TEPC, and the key factors affecting the effective gain are the voltage of GEM electrode, the drift area field, collected area field, the gas components filling into sensitive area and the gas pressure.Three dimension distribufion of electric field in GEM-TEPC were simulated with code ANSYS, and the way how to simulate the maximum safe gain of GEM-TEPC with code Garfield and the way how to measure the maximum safe gain were studied.

Key words: GEM-TEPC, Electric field, Effective gain, ANSYS, Garfield