The invention provides a device for inflating an air-floating platform by utilizing wave energy. The device comprises a base (21) which is fixed on the outer side wall (12) of the air-floating platform, a floater (31), a pressing plate (33), an inflator (40), an air conveying pipe (51) and an air suction pipe (61); when the pressure of an air cushion is not sufficient, most part of the floater (31) is located below a water surface; under the effect of waves, the floater (31) can drive the pressing plate (33) to upwards and downwards or leftwards and rightwards rotate around a spherical hinge (34) or push and pull the spherical hinge (34) to move back and forth; and the piston rod (42) of the inflator is pushed to inflate the air cushion through the air conveying pipe (51). Under the reciprocating effect of the waves, the air cushion can be inflated continuously until the air pressure of the air cushion is restored to a rated value and the platform floats to normal load draught; and at the time, most part of the floater (31) is exposed out of water, and the device stops working. By adopting the device, the air pressure of the air cushion can be maintained at the rated value so that requirement on the performance of the platform is met.