Based on the fiber with sub- wavelength aperture,the point- diffraction wavefront with both high numerical aperture (NA) and high power is obtained,by which the poor light power of pinhole point diffraction wavefront and the small aperture angle of single-mode fiber point diffraction wavefront can be solved.We analyze the point- diffraction wavefront based on the finite difference time domain (FDTD) method,and the effects of various factors such as aperture,cone angle,film thickness of sub-wavelength-aperture fiber and NA on pointdiffraction wavefront error,aperture angle,light transmittance and intensity uniformity are discussed in detail.The simulation results show that an aperture angle about 90° and light transmittance about 29% can be obtained with 0.5 mm sub-wavelength fiber aperture,and the corresponding testing precision is better than root mean square value 0.0011 λ within 0.60 NA.The simulation demonstrates the feasibility of high NA and high power of point-diffraction wavefront,and provides theoretical basis for choosing the dimension of sub-wavelength-aperture fiber in practical system design.