The door and frame of civil aircraft transfer loads through face-to-face contact between interface parts, while the interface clearance affects the load distribution, thus it’s quite crucial for flight safety. However, there is a lack of interface clearance and its influence on load distribution in existing studies, and also design method of interface clearance in engineering. In this paper, a design method of interface clearance is proposed, which essentially is a Monte Carlo simulation based on clearance randomness. A detailed finite element model of both door and frame is established, in which the linear gap and the Direct Matrix Input Grid are introduced, the load distribution affected by the clearance randomness is analyzed. In simulation, design basis and mathematical describing method of the interface clearance are determined, and finally design boundaries with 95% reliability are given. The method provides a theoretical foundation for the interface clearance design.