In this paper, we study an optimal investment strategy for defined contribution pension plan with inflation under Knightian uncertainty. Firstly, we obtain the dynamics of consumer-basket-price with inflation by using It\^o formula. Secondly, we establish the wealth dynamic equation for an agent, and characterize the agent's expected utility function by the stochastic control theory, where the agent has different levels of ambiguity aversion to different companies. Thirdly, we get the HJB equation, from which we obtain the explicit form solutions of the optimal investment strategy. Finally, we analyze the impacts of the ambiguity and the inflation on the optimal investment strategy of an agent through a numerical simulation.