A pressure-adjustable pneumatic system of a soda machine, comprising an upper cover, an air inlet support, an air distribution valve, a sub-machine support, a safety valve, and a piston-type pressure driving device, wherein the air distribution valve comprises an air inlet cavity, an air inlet interface communicated with the air inlet cavity, an exhaust cavity surrounding the air inlet cavity, an exhaust driving pipeline communicated with the exhaust cavity, and an exhaust valve provided on the exhaust driving pipeline, the exhaust driving pipeline is provided with an interface, the piston-type pressure driving device comprises a cylinder with an open end, an air inlet interface provided at the air inlet end of the cylinder, a piston, a sealing rubber plug, an ejector rod connected with the piston, a spring and a push rod nut, wherein the open end of the cylinder is provided with internal threads; the push rod nut comprises a body part, an operating part surrounding the body part, an upper guide hole provided on the body part and a counter hole; the body part /941) comprises an external thread part and a sealing part; the sealing rubber plug is provided at one end of the piston, the sealing rubber plug is fitted with the closed air inlet of the cylinder, the spring is sleeved on the ejector rod, the external thread of the push rod nut is screwed with the internal thread of the cylinder; the spring extends into the counter bore, the ejector rod extends through the upper guide hole, the piston-type pressure driving device is fixed on the air inlet support, the air inlet interface is inserted into the interface; the sub-machine support is connected with the outer cover and the lower end of the air inlet support; wherein the upper cover is provided with a knob hole; the operating part is provided with a shaft head; the air inlet support is provided with a circular counter bore, the bottom plate of the circular counter bore is provided with a through hole, and the through hole is opposite to the shaft head; characterized in that the system further comprises a driving base, a knob, a driving gear, a driving wheel set, a driven wheel set, and a drive gear; the driving base comprises a circular base cavity, a driving wheel set base and a driven wheel set base, wherein the circular base cavity is communicated with the driving wheel set base; the driving wheel set comprises a first gear, a second gear and a fixed shaft; the driven wheel set comprises a speed reducing wheel, a driven wheel and a rotating shaft, the driven wheel comprises a shaft body, a cylinder with an open lower part and teeth provided at the open end of the cylinder; the driving base is fixed on the air inlet support, the lower shaft body of the driving gear is rotatably fitted with the bottom plate of the circular base cavity, the connecting rod at the upper end is connected with the connecting part of the knob; the first gear and the second gear are provided vertically and pivotedly connected to the driving wheel set base by means of the fixed shaft, the first gear is engaged with the driving gear; the rotating shaft is rotatably fitted with the driven wheel set base, the upper end of the rotating shaft is fixedly connected to the speed reducing wheel, and the lower end of the rotating shaft is connected to the shaft body of the driven gear; the drive gear is fixedly connected to the shaft head, the drive gear extends into the circular counter bore through the through hole, and the driven gear is located in the circular counter bore and engaged with the drive gear; and a handheld part of the knob extends out of the upper cover through a knob hole. characterized in that the system further comprises a driving base, a knob, a driving gear, a driving wheel set, a driven wheel set, and a drive gear; the driving base comprises a circular base cavity, a driving wheel set base and a driven wheel set base, wherein the circular base cavity is communicated with the driving wheel set base; the driving wheel set comprises a first gear, a second gear and a fixed shaft; the driven wheel set comprises a speed reducing wheel, a driven wheel and a rotating shaft, the driven wheel comprises a shaft body, a cylinder with an open lower part and teeth provided at the open end of the cylinder; the driving base is fixed on the air inlet support, the lower shaft body of the driving gear is rotatably fitted with the bottom plate of the circular base cavity, the connecting rod at the upper end is connected with the connecting part of the knob; the first gear and the second gear are provided vertically and pivotedly connected to the driving wheel set base by means of the fixed shaft, the first gear is engaged with the driving gear; the rotating shaft is rotatably fitted with the driven wheel set base, the upper end of the rotating shaft is fixedly connected to the speed reducing wheel, and the lower end of the rotating shaft is connected to the shaft body of the driven gear; the drive gear is fixedly connected to the shaft head, the drive gear extends into the circular counter bore through the through hole, and the driven gear is located in the circular counter bore and engaged with the drive gear; and a handheld part of the knob extends out of the upper cover through a knob hole.