Abstract: Grain insurance belongs to policy-guided agricultural insurance. Accurate rate-making will be conducive to the policy-making of agricultural insurance. Grain catastrophe events belong to extreme value events, so the study is based on extreme value theory. The paper regards GPD as the tail distribution of grain calamity loss data after diagnosis. The GPD parameters are estimated by maximum likelihood. According to the thought of Loss Expectancy Method, the paper probes into the net premium rate calculation method of grain catastrophe insurance. And then an empirical study is done on the net premium rate calculation of grain catastrophe insurance in major producing areas in China. The results state the net premium rates are high and different from others in these areas and the north's is higher than the south's on the average level of net premium rates. According to the results, the policy recommendations are made that the Government should support grain catastrophe insurance of major producing areas and the subsidy sum should be proportional to the premium rates in these areas and the supportive degree to the north should be bigger than to the south relatively.