Heave compensators are widely used in offshore equipments to decouple the load motion from the wave induced ship motion. Hydraulic transformer based heave compensator (HTHC) can better compensate the ship’s heave in comparison with passive heave compensators (PHC) under changing sea conditions, meanwhile the accumulators’ volume is decreased significantly. Here in this paper, some further discussions about HTHC are given on the aspects of prediction, controller design and energy saving through simulation. Results turn out that heave prediction based on sliding mode observer is better than the Luenberger observer based one; chattering can be reduced through back-stepping method. The controller is robust when the load is perturbed by uncertain forces, and energy consumption of HTHC is about 56% of the one in an equal-sized hybrid active heave compensator (HAHC) meanwhile its total installed power can be reduced by 70%.