Provided is a 3D printing assisted forming method for a fiber reinforced composite material. An FDM 3D printing forming method and a continuous fiber composite material forming method are combined, a prepreg coating and an assisting material are laid on the surface of a part in a prepreg-vacuum bag molding composite material forming mode with an FDM 3D formed part as a forming mold, curing of prepreg is completed under a certain degree of temperature and pressure, and a supporting material is removed, cleaned and dried. By integrating the advantages of the flexibility and high precision of FDM 3D printing forming and the advantages of low weight and high strength of the composite material, the defects that FDM 3D printing forming is low in strength while the composite material is can not be separated from the mold easily are overcome, and the fiber reinforced composite material of a complex structure can be formed and manufactured into parts.