The invention provides a preparation method of a foam board for decoration. The method comprises the following steps that modified phenolic resin, a surfactant, organic acid, an emulsifying agent anda foaming agent are mixed for reaction; sodium hydroxide is added for regulating the pH to obtain a first mixture; b, melamino-formaldehyde resin, silicon dioxide, carbon black and aluminum hydroxideare added into the first mixture; stirring and ultrasonic dispersion are performed to obtain a second mixture; c, a foam stabilizer is added into the second mixture; heating reaction is performed; then, vacuum dehydration is performed to obtain a mixture; d, the third mixture is guided into a mold; curing formation is performed. The prepared foam board has good mechanical and fireproof performance, and has the characteristics of light weight, heat preservation, heat insulation, low heat conducting coefficient, low water absorption rate and the like.