The invention relates to the field of printers, in particular to an FDM type 3D printing method. An FDM type 3D printer adopted by the method comprises a charging mechanism, a movable mechanism, a supporting mechanism, a clamping mechanism, a spraying mechanism and a waste collection mechanism. Melt charges in different colors can be added into the spraying mechanism conveniently through the charging mechanism. The spraying mechanism is driven by the movable mechanism to move conveniently. Materials needing to be printed can be supported by the supporting mechanism. Materials with different diameters can be sprayed by the spraying mechanism. Waste caused by pigment replacement can be collected by the waste collection mechanism. The materials in various colors are arranged in a bulking cavity separately, then electromagnetic valves at the correspondingly positions are opened as required, thus, melting charges of needed pigments can fall for printing, operation is convenient, color changing of the melting charges can be achieved for meeting different demands by switching the electromagnetic valves, and the application range is wide.