Abstract In these years, Value at Risk (VaR) has been an important tool of risk management in the bank industry. In the past, property and casualty insurance industry does not have many correlation research in this aspect, especially in the key of the underwriting risk application may be collection difficulty in data , the domestic correlation research literature were actually few. In this paper, we use TEJ data bank to study the statistical data which needs for the research , the research sample total has 9 property insurance companies, By using the public information of TEJ data bank, it obtains the yearly and quarterly data, and uses the ¡§Fuzzy Distance Weighting Method¡¨ to change the quarterly data into monthly data , calculates loss ratio of the yearly, quarterly, monthly, then use the idea of VaR to compare the different of loss ratio-at-risk in yearly, quarterly, monthly¡CMoreover this study discusses the underwriting risk influence factor of domestic property and casualty insurance industry .This research discovers that yearly data will underestimate the actual of loss ratio at risk . In addition using regression analysis, the underwriting loss ratio-at- risk is influenced by free cash flow , leverage ratio , and firm size. According to the result of this paper, it could provide the reference rule when property and casualty insurance industry or supervisory authority set up the risk management rule. Keywords: Value at risk, Loss ratio, Loss ratio-at-risk, Underwriting risk