To achieve the online correction of the misaligned error of large aperture thin film splicing mirrors, an imaging model comprising five pieces of Fresnel lens was established herein. By analyzing the point spread function (PSF) and the modulation transfer function of the optical system in the presence (MTF) of the misaligned error, the relationships between the misaligned error and PSF as well as MTF were obtained. The stochastic parallel gradient descent (SPGD) algorithm was used to correct the misaligned error online. To verify the performance of the proposed algorithm, five performance evaluation functions, including sum of square of far-field light intensity, equivalent radius of far-field light spot, power in barrel, MTF integral, and second-order moment of light intensity, were selected as optimization indexes to correct the misalignment error, and the convergence speed and accuracy of evaluation indexes were compared. The correction results of 100 random errors show that the five indexes can convergence, and the root mean square values of the corrected wavefront are less than 0.13λ and the Strehl ratio is greater than 0.96. The MTF integral and the second-order moment of light intensity converge fastest, and the precision of the equivalent radius of far-field facula index is optimal.