It needs supernumerary overhead to prove the correctness of computation results in traditional delegation computing, that cause less efficient and high overhead. This study addresses these problems, proposes a rational delegation computing protocol based on rational trust model by combining the thinking of game theory and rational trust modeling. In order to ensure the reliability of computation results, appropriate utility function incentive calculator is set up to execute protocol honestly. Firstly, construct the rational trust model based on the thinking of rational trust modeling. The lifetime of server is taken as parameter to design the utility function which contented profit of participants of delegation computing; analyze behavior strategy of participants in protocol further, when they take "honest" strategy, they can earn the point of Nash equilibrium. Secondly, design rational delegation computing protocol by combining Pedersen commitment scheme and NTRU public key cryptosystem, with the advantage of high speed, high level security, and ability of resistant to quantum computing attacks. Finally, this protocol is analyzed from three aspects:correctness, security, and performance, and affection of the lifetime on the utility of participants is proven through experiment, the outcome shows reliability of computation results can be ensured effectively by the proposed protocol.