The invention discloses a blade root structure optimization method of a dimensionality reduction simulated annealing algorithm. The method includes the steps that firstly, a design variable in the optimization process is determined, and two-dimensional parameterization modeling and three-dimensional parameterization modeling of a target blade are completed; secondly, an N0 set of design variables is randomly generated, an initial average value mu0 and an initial standard deviation delta0 of maximum stress value relative errors of a two-dimensional model and a three-dimensional model under the N0 set of design variables are calculated through a finite element method; thirdly, according to a computation result of the three-dimensional finite element model, the blade root is optimized through the simulated annealing algorithm, a dimensionality reduction rule is introduced according to the initial average value mu0 and the initial standard deviation delta0 of the relative errors in the Metropolis sampling process, the finite element computation amount is reduced, and the average value and the standard deviation of the relative errors is updated after three-dimensional model computation is conducted; when the annealing temperature is lower than a set value or a target function value is stable, the computation process is converged if the result is verified to be within a permissible error range, and optimization is completed. The method has the advantages of being high in convergence speed, capable of saving computation resources and time and the like.