Considering the facts that the data are not high frequent ones and the business lines are more than two，the copula models used to construct the joint distributions in market risk measurement are not completely applied to the underwriting risks measurement，this paper constructs a comonotonicity model to tentatively dis_x005fcuss how to measure the economic capital for underwriting risks combined with the characteristics of the underwriting risks．The paper uses a real property insurance to show the process of the assessment process of the underwriting risks．In the empirical analysis，the paper also compares the comonotonicity model and the copula model．Empirical results show that both the comonotonicity model and the copula model can measure the diversification of the business lines． However，the comonotonicity model can get more accurate results than the copula model．