Double insurance derives from the Principle of Indemnity. In order to establishment the system of validity of double insurance, we must consider five main factors such as prevent over insurance, avoid unjust enrichment, control moral hazard, strengthen the security and balance the interests. The validity of the double insurance inc1udes internal validity and external validity. Double insurance should be divided into good faith double insurance and malicious double insurance. As to the validity of good faith double insurance, we should use the provisions of joint and several indemnification for reference. On the other hand, the contract of malicious double insurance is invalid. As to the external validity of double insurance, we should adopt independent 1iability. At the same time, we should authorize policy-holder in good faith double insurance to eliminate double insurance.