The invention discloses a sealing structure and method of a front steam seal of a high-intermediate pressure combined cylinder of a turbine. The sealing structure comprises a steam press, the high-intermediate pressure combined cylinder and low pressure cylinders. The low pressure cylinders are symmetrically arranged in a double flow manner, the high-intermediate pressure combined cylinder is arranged in a double flow manner, and the steam press and the turbine are coaxially arranged. The rear end of the high-intermediate pressure combined cylinder is connected with the steam inlet ends of thelow pressure cylinders, and the steam outlet ends of the low pressure cylinders are connected with a steam condenser. The front end of an inner cylinder of the high-intermediate pressure combined cylinder is connected with the steam press, and the outlet end of the steam press is connected with the front steam seal of the high-intermediate pressure combined cylinder. The steam inlet end of the steam press communicates with the steam exhaust end of a high pressure cylinder, and the steam exhaust end of the steam press communicates with a front steam seal of a high pressure inner cylinder. Thesealing method comprises the following steps that 1) complete machine through flow calculation is carried out; 2) the thrust difference value of axial thrust generated by the turbine and thrust capable of being balanced by a thrust baring is calculated; 3) steam press through flow calculation is carried out; 4) axial thrust generated by a movable blade of the steam press is calculated; 5) axial thrust of a rotor of the turbine is subjected to balance calculation; and 6) the heat rate is calculated through unit heat balance.