The invention provides a preparation method of a GaN-based laser and AlGaN/GaN HEMT integrated device. The method comprises the following steps of S1, preparing a GaN-based laser on a GaN-based lasersubstrate layer, and preparing a first AlGaN/GaN HEMT epitaxial wafer on a first substrate; S2, performing sequential etching in a dry etching manner to obtain a mesa structure, an AlGaN/GaN HEMT transfer region and an AlGaN/GaN HEMT mesa structure of the laser; S3, removing the first substrate of the first AlGaN/GaN HEMT epitaxial wafer in a wet etching manner to obtain a second AlGaN/GaN HEMT epitaxial wafer; S4, transferring the second AlGaN/GaN HEMT epitaxial wafer to a second substrate to obtain a third AlGaN/GaN HEMT epitaxial wafer; S5, bonding the third AlGaN/GaN HEMT epitaxial wafer with the GaN-based laser by an adhesive material; and S6, preparing a passivation layer and electrodes. The method avoids the technical problems of poor isolation and low safety of an original preparation method and realizes the technical effects of high safety, high frequency resistance, high voltage resistance and easy mass production of a device system.