The invention provides a steam-liquid full-flow screw power machine with an axial force balancing device. An axial force balancing device body (9) is arranged in a low-pressure end seat end cover (20), the axial force balancing device body (9) is composed of a pressure-bearing sleeve (6) fixedly connected to the shaft end of a driving shaft (4) in a sealed mode and a plunger piston (7) fixedly connected to the low-pressure end seat end cover (20), wherein an oil inlet hole (71) is formed in the plunger piston (7), the oil inlet hole (71) is connected with an oil pump arranged outside a machineshell through an oil-conveying pipe (72), the inner ring surface of the left end (61) of the pressure-bearing sleeve (6) is in sliding fit with the outer circle surface of the right end (73) of the plunger piston (7), and the pressure-bearing sleeve (6) is used for forming a hydraulic cavity (70) with the plunger piston (7). The pressure in the hydraulic cavity (70) produces axial thrust on the pressure-bearing sleeve (6) and the shaft end surface of the driving shaft (4) to jointly conduct the axial thrust action on the driving shaft (4), axial force generated by a driving screw rotor (41) to the driving shaft (4) during working is overcome, and that is, the axial force of the driving shaft (4) is balanced.