Abstract: To meet various control requirements, a control system was designed and the control strategy was proposed for single piston HFPE engine. Aiming at the difficulties of adjustment and control piston position when starting up, the position of piston's bottom dead center (BDC) was corrected and controlled according to the characteristics of hydraulic free piston engine. Test of developed control system gives the following results. The control system could realize frequency control of HFPE starting and continuous operation with reasonableness and reliability. The presented control strategy is rational and feasible. The correction of controlling piston's BDC position is improved so that the ability of piston return could be guaranteed under abnormal circumstances. The control of variable compression ratio could be achieved and the performance of cold starting and cylinder combusting is enhanced.