The invention relates to a height adjusting device for a material clamping mechanism and a height adjusting method thereof. The height adjusting device comprises a rocker arm mounting base (4), a rocker arm (1), an adjusting screw (6) and an ultra-thin air cylinder (5), wherein a pin shaft (2) is fixedly arranged on the rocker arm mounting base (4), the rocker arm (1) is arranged on the pin shaft(2) in a rotating mode through a bearing (3), the ultra-thin air cylinder (5) is arranged in a sliding groove of the rocker arm mounting base (4) in a sliding mode, and the like. The height adjustingdevice and the height adjusting method thereof have the advantages that the height volume of the material clamping mechanism is changed by adjusting the mounting position of a linear driving element,the structure is simple, the adjustment is convenient, and the cost is low.