The utility model discloses a water film device of protection pneumatic cylinder, the water film device is including installing the protector on the piston rod and installing the 2nd protector on the cylinder body, a protector with the 2nd protector passes through the elastic membrane and connects. The utility model discloses a low temperature air circumstance that two floor height pressurized-water curtains protection elastic membrane, this elastic membrane can further protect hydraulic cylinder piston rod to be in dry steady pressure protects hydraulic cylinder piston rod not receive the hyperthermia radiation, not washed out by moisture and granule, and impurity and moisture can be through inside the sealed entering pneumatic cylinders of piston rod simultaneously, improvement hydraulic system's stability, just the utility model discloses a cascade has adopted the elastic membrane, can not produce the spare parts expense, the low price, and the device effect is obvious.