A risk assessment model on agricultural natural disaster insurance is established, taking wheats for example. Firstly, estimate the disaster probability of wheats which suffered from gale, hail, waterlog and frost in each growing season. Secondly, calculate compensation expectations of wheats damaged by different natural disasters by insurance companies under the existing insurance scheme. Thirdly, it is obviously that insurance companies actually run in a loss comparing with the companies' net income in the existing insurance policy. AHP is used to establish a Cost-Sharing Model based on the government, insurance companies and farmers Satisfaction Degree Equation. By solving the equations of satisfaction, getting the tripartite risk ratio under the greatest satisfaction degree are 0.44, 0.19 and 0.37, respectively. And a new insurance scheme is developed. The results indicate that the companies can operate normally when the loss probability is 0.147 under the new scheme, it is to see the new insurance scheme is effective and feasible.