The invention provides a preparation method of H-ZSM-11 modified molecular sieve catalyst. The H-ZSM-11 modified molecular sieve is compounded through a one-step hydrothermal method; the H-ZSM-11 modified molecular sieve prepared by the invention can effectively improve the reaction from methanol to low carbon olefins (MTO). The methanol conversion rate of the prepared H-ZSM-11 modified molecularsieve catalyst in the MTO reaction is 57-85%, the selectivity of low carbon olefins is 45-70%, and the yield is 32-57%. The methanol conversion ate in modified H-ZSM-11 modified molecular sieve catalyst in the MTO reaction is up to 97%; the selectivity of the low carbon olefins is improved by about 10%, and the yield is improved by about 20%; the catalyst is good in thermal stability, and cannot be deactivated rapidly within a short time.