The invention discloses an offshore auxiliary construction platform device and a using method thereof. A crane system is arranged on a movable support system; the support system comprises two parallel rail beams; a horizontal connecting beam vertical to the length direction of the rail beams is arranged between the two rail beams; the rail beams and the horizontal connecting beam have a box girder structure; two box girders are vertically connected by a diagonal bracing; a bearing platform under the rail beams is provided with a box girder support; a support system is driven to move by a travel mechanism; and the travel mechanism is that a tetrafluoro sliding plate is arranged above the box girder support, the bottom of a bottom flange of a box girder is paved with a stainless steel plate facilitating the mass movement of the platform device, and the stainless steel plate moves on the tetrafluoro sliding plate and is dragged by a traction mechanism positioned on the end parts of the rail beams. The platform device can automatically move to the next working face from one working face, avoid frequent assembly and disassembly and transportation of equipment, reduce safety risks of offshore construction, and improve the efficiency of offshore construction of pier studs.