Abstract: Fission numbers of ²³⁵U samples irradiated in short time were obtained by fission yield method. The total emission rate of high-energy delayed γ-rays above 3 MeV per fission over time was measured by large volume NaI detector, and high-energy delayed γ-rays emission rate of pulse irradiation was gained. Fission numbers of two ²³⁵U samples were obtained by applying the emission rate of high-energy delayed γ-rays per fission, and the relative uncertainty is less than 4%