The mobile edge computing (MEC) yields significant paradigm shift in wireless communication, and the relay communication is a key technology for beyond 4G, the combination of the two techniques is proved to provide better service to the users recently. To handle the offloading decision and relay selection problems for relay assisted MEC system, the incentive mechanism design and resource allocation for relay assistant MEC system is discussed in this paper. More specifically, the system design involves the offloading decision, relay selection, and the relay incentive mechanism design. At first, a virtual currency pricing scheme is proposed as the incentive mechanism to encourage the relays' cooperation, and then we discuss the offloading decision, relay selection and pricing optimization for the relays. Due to the formulated problem is mixed integer non-linear programming (MINLP) and it is difficult to solve. Therefore, a dynamic virtual currency pricing based distributed matching algorithm is proposed and its performance is verified by numerical analysis. The simulation results indicate that, compared with the other three benchmark algorithms, the proposed matching algorithm obtains the best complexity and performance tradeoff.