A pitch adjustment device for blow molding machine is disclosed, which comprises: a platform, a driving unit, a screw rod unit, and a plurality of clipping units. The screw rod unit is composed of a transmission mechanism and a screw rod, in which the screw rod is pivotally mounted on the platform in a manner that when the platform is driven to move, the moving platform will activate the transmission mechanism for bringing along the screw rod to rotate. In a preferred embodiment, the screw rod has a plurality of guide slots formed thereon in a manner that, for any two neighboring guide slots, the two pitches measured between corresponding ends of the two neighboring guide slots are different from each other, so that when the platform is driven to move in a rectilineal motion reciprocatively which brings along the screw rod to move and rotate accordingly, the pitches between the plural clipping units are varied accordingly as the plural clipping units are disposed at positions corresponding to the guide slots, and thereby, the pitches between any two neighboring bottle embryos hold by their corresponding clipping units are varied.