Abstract: Shanxi Zhongfu Nuclear Instruments Co.,Ltd.(CIRNIC) has independently developed and produced various types of large area gas-sealed proportional counter of 40-600 cm².An experiment focusing on background count rate,plateau curve,surface emission rate response,coefficient of variation and other physical characters,on one of the device of which with 517 cm² effective area has shown that under the same testing environment and experimental conditions,background count rate is 24.5 cps,surface emission rate 50.4%,coefficient of variation 0.85%.

Key words: gas-sealed proportional counter, plateau curve, surface emission rate response, coefficient of variation