Abstract: In this paper, the linewidth of femtosecond laser two-photon polymerization is studied by the theory of free radical density and the effect of optical tweezers. Based on the relationship between free radical density and time in the process of two-photon polymerization, the expression of linewidth of two-photon femtosecond laser processing is deduced considering the effect of optical tweezers. The relationship of linewidth with scanning speed and laser power is studied and the influence of different light initiators on the linewidth is also discussed. The theoreticial result agrees well with the experimental one in the literature. The result of this paper gives a new idea for the study of femtosecond laser two-photon processing, and provides a theoretical formula for the study of the influence of optical tweezers on linewidth.