As a novel imaging technique,Fourier single-pixel imaging has potent ial applications in many fields such as 3D imaging.In order to promote the application of Fourier s ingle-pixel imaging, we investigate the impact of light source defocusing on Fourier single-pixel im aging and its optimization strategy in this paper.Applying Gaussian model to describe the def ocusing,we analyze theoretically Fourier single-pixel imaging with defocused light source.Then em ploying digital light projector modulated by Fourier basis pattern as the light source,we investigate the influence of the defocusing on the peak signal-to-noise ratio PRSN of Fourier single-pixel imaging by changing the defocused parameter of the light source.The results show that the more the ligh t deviates from the focus of light field,the worse the imaging quality.Correspondingly,the PRSN of the reconstructed image decreases from 28.4 dB to 20.5 dB.In terms of this prob lem,we explore an adaptive strategy to optimize the defocused image which combines adaptive filter with blind deconvolution,the PRSN of the optimized image improved b y 1.4—4.0 dB.It is helpful to the application of Fourier single-pixel imaging in complex environments such as lon g-distance imaging.