In order to study the effect of convolution effect and fabrication errors on the axial focusing characteristics of low F-number diffractive optical elements (DOE) with continuous relief fabricated by laser direct writing,a theoretical model is established using Rayleigh-Sommerfeld diffraction theory to describe the influence of the structure parameters,the diameter of the writing spot,the interscan distance and the fabrication errors on the diffraction focusing characteristics of low F-number DOE with continuous relief,and continuous-relief DOE with a design wavelength of 441.6 nm,a F-number of 4 and a phase depth factor of 3 are fabricated and measured.The good agreement between theoretical and experimental results verifies the validity of the diffraction model established.