Based on the off-axis lensless Fourier transform digital holography principle，two main determining factors,which effect the imaging resolution of the Fourier transform digital holography are discussed in this paper.One is the recording distance and the size of the object.The other is the size of reference light source.The 1.0×1.0 mm2 and 1.5×1.5 mm2 areas in the center of an USAF 1951 Style Resolution Target serve as the objects.Corresponding experiments are performed employing three reference light sources with the sizes 2 μm,6.5 μm and 15 μm respectively,at different recording distances.Both the theory and the experimental results show that as in meeting three terms (twin images and zero order in reconstructed image) separation from each other and sampling theorem conditions,shortening the recording distance or decreasing scale of the reference light source may improve the system resolution of lensless Fourier transform digital holography of micro object.