As the traditional voltage sag mitigation schemes cannot solve the waste problem of mitigation capacity, a new method of allocation plan of voltage sags mitigation devices based on life cycle cost is presented in this paper. According to the mathematical model of series and parallel mitigation devices (such as DVR and STATCOM), the differences of mitigation characteristics between those devices are analyzed. Considering the investment cost and economic benefit of the mitigation schemes, allocation plan schemes of voltage sags mitigation devices are obtained. The proposed method has been applied to IEEE 33-bus test system and compared with the traditional mitigation schemes. The results validate its economy and practicality when there are several sensitive loads in the distribution network. This work is supported by National Natural Science Foundation of China (No. 51577115).