In view of the systemic risks encountered by policy holders in the insurance process, the optimal surrender strategy of DB pension plan based on random inflation risk is studied. The scheme has a minimum protection function, and policy holders can exercise surrender options at any time. In order to find the best time to exercise surrender option, the optimal exit time of DB annuity plan with surrender option can be transformed into a free boundary problem. From this, a corresponding nonhomogeneous partial differential equation can be obtained. After the integral transformation of the nonhomogeneous partial differential equation is carried out by using Merlin transformation, the integral equation is solved by RIM recurrence integration method, and an integral equation and the optimal exit boundary of surrender option estimation are obtained. The research shows that this option provides more protection for the policy holder and makes the policy holder have more options. In addition, we use numerical analysis to give the nature of fair rate and the influence of different investment ratios on account value, as well as its optimal surrender strategy.