An IM-5 molecular sieve synthesis method comprises the following steps: 1, dissolving an inorganic alkali, an aluminum source and a template in deionized water, and uniformly mixing to prepare a mixed solution; 2, adding a solid silica gel to the mixed solution obtained in step 1, adding a template precursor, and uniformly mixing to prepare a colloid or a solid-liquid mixture; and 3, transferring the colloid or solid-liquid mixture obtained in step 2 to a crystallization kettle, carrying out hydrothermal crystallization for 1-10 days, cooling after the crystallization to obtain a mixed liquid, and washing, filtering and drying the mixed liquid to obtain raw IM-5 molecular sieve powder, wherein reactants comprise SiO2, Al2O3, M2O, R, A and H2O, a molar ratio of SiO2:Al2O3:M2O:R:A:H2O is 60:(0.3-6):(6-20):(4-15):(1.2-6):(300-1200), M2O is an alkali metal oxide, R is the template, and A is the template precursor. The IM-5 molecular sieve synthesis method has the advantages of good product repeatability, effective reduction of the water content, increase of the concentration of the template, crystallization time shortening and single kettle yield increase.