The invention discloses a method for improving error detection precision of a sparse aperture imaging system under Gaussian noise. The method comprises the steps of: acquiring a Fisher matrix about the sparse aperture imaging system based on a log-likelihood function of two images in a phase difference method, and acquiring evaluation factors through inversion of the Fisher matrix, acquisition of a trace of the inversed matrix and statistical analysis; and calculating corresponding evaluation factors through changing external parameters such as defocusing amount of a focal plane image and the number of photons received by a focal plane and a defocused plane, wherein the smaller the values of the evaluation factors are, the higher the precision of detecting errors of the sparse aperture imaging system by using the parameters when the phase difference method is adopted. The method provided by the invention can provide a basis for selecting the optimal phase difference method parameter configuration, and effectively improves the error detection precision of the sparse aperture imaging system.