Capacity adjustment of Gas Engine-Driven Heat Pump (GEHP) can be achieved by controlling engine rotary speed. The goals of rotary speed control are to maintain the rotary speed within a setting range, robust with respect to disturbance and match the rotary speed and cooling/heating capacity. In order to control the rotary speed of gas engine effectively, the rotary speed knowledge base and controlling rules module were established and a rotary speed expert controller was designed according to the historical data and expert experiences in this study. Simulation research was carried out with the conduction of the expert controller and the results indicated that the rotary speed fluctuations caused by instant load can be reduced effectively, the rotary speed operation was smooth and had no overshoots with an acceptable response during the capacity adjustment process, thus it holds a good performance with respect to disturbances theoretically. The expert controller had been applied to engine rotary speed control in a GEHP system experimentally in different conditions, which was testified that the expert controller played a better performance small overshoots, flat output and reduced action time, less than 15 s, rotary speed was stable when turning on the clutch of compressor. Therefore, the expert controller can suppress the disturbance effectively, and improve the control quality observably. (C) 2013 Elsevier B.V. All rights reserved.