A simplified methodology is described for identifying human pilot describing function in a two-axis control task. A real time simulation is carried out on simulator, in which pilot tracts the command velocity and pitch angle of aircraft by controlling the stick and throttle respectively. Coherence functions between the two-axis show a weak coupling in this task. This suggests it is possible to treat the two-axis control system as two single axes respectively for the pilot model identification for the longitudinal control task. The feasibility and rationality of simplified methodology is demonstrated in both theory and simulation experiment for the control task.