The invention relates to an opposed hydraulic free piston engine with a hydraulic synchronizing mechanism and a driving method of the opposed hydraulic free piston engine. The opposed free piston engine comprises a high-pressure working medium liquid path, a low-pressure working medium liquid path, an electronic control unit, an oil sprayer, a gas inlet, an exhaust opening, a first cylinder sleeve, a second cylinder sleeve, a first piston matched with the first cylinder sleeve, a first piston rod connected with the first piston, a first high-pressure working medium output cavity connected withthe other end of the first piston rod, a second piston matched with the second cylinder sleeve, a second piston rod connected with the second piston, a second high-pressure working medium output cavity connected with the other end of the second piston rod, a high-pressure working medium liquid path, and the hydraulic synchronizing mechanism, wherein the first cylinder sleeve and the a second cylinder sleeve are coaxial and symmetrically distributed According to the opposed hydraulic free piston engine with the hydraulic synchronizing mechanism and the driving method of the opposed hydraulic free piston engine, a first synchronizing cavity and a fourth synchronizing cavity of the hydraulic synchronizing mechanism communicate, and a second synchronizing cavity and a third synchronizing cavity communicate, so that two synchronizing loops are formed; and due to the property that a liquid working medium is difficult to compress, mutual containing and mutual restraining are achieved, and the pistons on the two sides can synchronously move.