The invention discloses a preparation method of synthetic wood. The preparation method includes the following steps that S1, preparatory work before starting up is carried out, and whether the water,electricity and gas of an extruder are normal or not is checked; S2, warming is started; S3, after setting a product process temperature to the specified temperature, the screw revolution of a host and the feeding screw rotation are adjusted, and the screw revolutions of the host and feeding screw are increased after die head discharging; S4, after die head discharging is stabilized, the top coverof a qualitative die is opened or a pulling wire is used for pulling; S5, a cold water pipe is added to a water tank, and the shaped material is subjected to cold water cooling; S6, the pressure of atractor is adjusted until the pressed material does not slip; S7, a calibrating table is moved forward to a certain position, and the pulling speed is increased or decreased appropriately; S8, the cutting size of a cutting saw is adjusted; and S9, the finished material is weighed. According to the preparation method of the synthetic wood, the produced synthetic wood meets the requirements of beautiful decoration and texture while can reduce use of wood, by adding bamboo powder and wood powder, the strength is increased, the produced synthetic wood is not prone to deform and fade, and the service life is longer.