Abstract: In the uncertain market environment, the firm's investment opportunities have the characteristics of option.In this paper the optimal contract design problem about real option investment is analyzed under principal-agent framework.The principal has the option to postpone the investment, the agent will execute the option granted under the principal-agent system.The agent has the motivation to hide information and transfer cash flow under asymmetric information.In order to maximize his own benefit, the principal will design contract.The agent will reveal truthful information under the contract.The real option models are established and the optimal contracts are given respectively under the symmetry and asymmetry information.Numerical analysis shows that, compared with symmetric information, the high cost project will be delayed to invest, the low cost project will be invested ahead of time, and the option value of the investment will reduce under asymmetric information.The option value of the principal will increase as audit efficiency improves.The more impatient the agent, the greater the option value of the principal.The study of this paper provides some guidance for the real option investment under principal-agent framework in reality.

Key words: real option, principal-agent, optimal contract, investment