The invention provides sorokin chlorella synthetic starch defect type mutant strains GT-1-SLM1, GT-1-SLM2 and GT-1-SLM3 through mutation screening. The preservation numbers of the strains are respectively CGMCC No.13861, CGMCC No.13862 and CGMCC No.13863, and the strains are preserved in the China General Microbiological Culture Collection Center. As related channels or a small part of the channels for synthesizing starch through the strains are blocked, the content of starch in cells is remarkably reduced, the grease synthesis velocity is remarkably increased, and the highest grease content in the cells is remarkably increased. By adopting the mutant strains provided by the invention, the microalgae oil generation period can be shortened, so that the risk of disease infection in the culture period can be reduced, and meanwhile as biomasses have relatively high content of grease, later grease extraction and preparation processes can be simplified, and high-quality germplasm resources can be provided for industrialization of microalgae oil production.