To provide a method for on-site preparation of a thermal press plate having no problem of storage lifetime and durability by incorporating higher performance than that of a precoating plate.

The method for on-site preparation of the press plate comprises a step of coating the plate with a composition containing a first heat sensitive substance having a shorter storage lifetime of about one month or less and a second substance mixed with the first substance to increase its infrared sensitivity, and a step of forming the image by exposing the plate by irradiating with an infrared ray within one month from the execution of the coating. The plate is directly provided for use in an on-press printer after the exposure.