Device-to-device (D2D) communication is efficient in traffic offloading in terms of transmission rate, energy cost, spectrum usage and etc. However, its unstable performance caused by spectrum reuse can drive users away, particularly when D2D users (DUs) are served as secondary users in cellular networks. Their low expectations on D2D services and frequent mode switch can block efficient D2D offloading, cause severe network congestion and result in poor quality of experience (QoE), especially in densely populated area. Hence, in this study, more than reducing the price to attract users, we propose a quality of service (QoS)- insured pricing strategy to promote D2D communication. In specific, to model users' decision-making process under the uncertainty of D2D performance, we introduce Prospect theory (PT) that captures irrational factors such as reference point, probability distortion and risk-aversion. Then, we design an insurance contract with terms of service price and insured QoS level to popularize D2D services and optimize operator's profit. Based on theoretical analysis, we propose an optimal QoS-insure pricing strategy algorithm, and discuss the practical implementation of the proposed strategy. The simulation results demonstrate the impacts of operation settings, individual irrationality and network conditions on operator's net profit from D2D offloading, and show the efficiency of the proposed strategy.