In view of the accurate use of airfield clearance rules in the evaluation of airfield clearance condition, and the impact of the longitudinal slope configuration of runway on obstacle limitation surfaces according to the regulations, concepts of ideal model and application model for airfield clearance zone are put forward. In order to analyze the influence of the two models on airfield clearance condition evaluation, airfield clearance zone of threedimensional space enclosed by the plane of obstacle limitation surfaces and the corresponding limiting requirement of height is of consideration. An evaluation model of airfield clearance condition is proposed, calculating the limiting range of height and plane of threedimensional lump. Referring to this method, the coordinates of the slope restraining points in runway strip and the points where transitional surface beside two sides of runway strip intersect inner horizontal surface are analyzed and confirmed, and then the calculation models of threedimensional lump of clearance for runway strip, terminal clearance zone and side clearance zone are established. Thus, the procedure of airport clearance condition evaluation is written and applied to an example. The comparison of the results after evaluating airfield clearance condition can be seen: ideal model is a special case of application model, in which one can be selected based on the life cycle of the airport. The application model must be used after entering the stage of airport feasibility study. What’s more, there is a certain regularity to merit attention about the difference of obstacle limitation height caused by different height at both ends of the runway in application model.