A wavefront evaluation method based on sparse subaperture was proposed for the collimated wavefront of 300 mm aperture wavelength-tuned interferometer. The method used the wavefront data of sparse aperture to construct a uniform and equally spaced subaperture arrangement model and utilized the simultaneous fitting algorithm to realize the reconstruction of the full-aperture collimated wavefront. The change rules of subaperture spacing and subaperture size on the reconstruction accuracy were analyzed by the numerical calculation, and the optimized subaperture arrangement way was obtained. Finally, an optimized subaperture arrangement with a subaperture size of 10.8 mm and an adjacent subaperture center spacing of 9.72 mm was used for the sparse subaperture evaluation of 300 mm aperture collimated wavefront. The simulation results show that the optimized sparse subaperture evaluation wavefront residual peak valley (PV) value is 0.001 6 ${\rm{\lambda}}$ and the residual root mean square (RMS) value is 1.689 3e-4 ${\rm{\lambda}}$.