On the basis of principal_agent theory, strategy of quality control in supply chain under double moral hazard condition is discussed. When the supplier's costs which are invested in products' quality prevention and seller's costs which are invested in products' quality appraisal both are unobservable information,the supplier and seller may incur moral hazard after contracting. In order to reduce the double moral hazard, the incentive measurements are given: one is the penalty to supplier when supplier provi...