The invention discloses a four-layer-color synthetic resin block and a preparation method thereof. The four-layer-color synthetic resin block is formed by four layers of structures sequentially, each layer of the structures comprise components as follows: polymethyl methacrylate, iron oxide red, iron oxide black, iron oxide yellow, titanium white, methyl methacrylate and ethylene glycol dimethacrylate. The preparation method comprises the steps as follows: polymethyl methacrylate powder is dried at a temperature of 80-90 degrees; four layers of materials are prepared in proportion respectively, and each layer of the materials are required to be mixed uniformly and kneaded until doughing time, so that a plastic dough material is formed; four layers of the plastic dough material are subjected to hot-pressing and bounded together in order in a die, the hot-pressing temperature is 110-130 DEG C, and the hot-pressing time is 10-20 min; and the four-layer-color synthetic resin block after hot-pressing is subjected to heat treatment at a temperature of 80-90 DEG C for 10-12 h, so that a four-layer-color synthetic resin block product is obtained. A dental model or temporary crown bridge, which is processed through the four-layer-color synthetic resin block, is natural and vivid in developing, and the preparation method is simple.