Self-diffraction effect has very important applications in the field of femtosecond laser, such as to improve the temporal contrast of femtosecond pulses, to be used as the reference pulse of self-reference spectral interferometry, and as the signal of self-diffraction frequency-resolved optical gating, etc. However, in the self-diffraction signal of femtosecond pulses with a broadband spectrum angular dispersion exists obviously, which will limit the application of self-diffraction effect. In this paper, the self-diffraction signal angular dispersion of femtosecond pulses is obviously reduced, when a right-angle prism is located in the light path of an incident beam with an incident angle of 23° to the prism. The experimental result provides a useful reference for the application of the self-diffraction effect to the research of femtosecond laser pulse in the future.