The lighting mode has great influence on the resolution of optical imaging system. Based on the coherence theory of light field, the main factor which influence the imaging resolution of first-order autocorrelation imaging and the second-order autocorrelation imaging of intensity fluctuation via multi-frame speckle illumination are studied. The theory and numerical simulation results show that the transverse coherence length of speckle on the object plane and the resolution of first-order autocorrelation imaging and the second-order autocorrelation imaging of intensity fluctuation are not monotonic relationship. In addition, compared with the traditional incoherent imaging, the first-order autocorrelation imaging and the second-order autocorrelation imaging of intensity fluctuation can only slightly improve the imaging resolution. The result of second-order autocorrelation imaging of intensity fluctuation is just the sharpening of the result of first-order autocorrelation imaging, which can't further improve the imaging resolution.