Recent offshore oil and gas development work and/or geoscience research work need heavy offshorework such as setting heavy structure on the deep sea bed, piping connection in deep sea etc. In a long period work, heavy structure may be let suspended in the sea from a floater under large floater motion in rough sea because of inability of work. Heave compensator seems to be an effective measure to adopt to the above kind of offshore works and compensators are already put to practical use with air spring mechanism. Lately, active heave compensatorsare also researched and developed to get high compensation effect. However, in case of heave compensation while suspending heavy structure under large floater motion, non-linearity and resonance of the airspring and dynamic friction effect at the compensating mechanism tend todecrease the compensation effect or rather increase the danger during suspension. Therefore, in case of activecompensation in rough sea, above mentioned effects shall be counted in the system design to get effective com-pensation. In this paper, active heave compensator combined with air spring mechanism is studied considering nonlinear effect of air spring, friction at the compensating mechanism and elastic response of suspended structu-re. High performance of the active compensation is verified by the model test in waves corresponding rough sea.