The invention discloses an epitaxial material stress control-based GaN thick film self-separation method, which comprises the following steps of: pretreating a substrate material; growing an epitaxial material on the substrate, gradually modulating process conditions to ensure that the stress of the epitaxial material is gradually concentrated to a preset self-separation position; when the thickness of the epitaxial material reaches the preset self-separation position, and performing jumping modulation on the process conditions to ensure that the stress is jumped at the preset position; gradually modulating the process conditions again to ensure that the stress of the epitaxial material is gradually released along with the increase of the thickness, namely the stress is reversely concentrated to the preset position; and finishing the epitaxial growth, and gradually reducing temperature to make stress difference on the two sides of the preset self-separation position further amplified so as to realize the self-separation of the monocrystalline thick film at the preset position. The method can effectively control the integral distribution of the stress in the epitaxial material and well realize the self-separation of the epitaxial material on the basis of ensuring the quality of the epitaxial material.