Abstract: The pulse signals of the output of preamplifier from the scintillator detector (NaI(Tl), CsI(Tl) etc.) have a long rising time, which causes the serious ballistic deficit existing in the process of the charge collection. In order to reduce the influence of the ballistic deficit on the energy resolution in the later pulse shaping, generally, a wide flat-toped shape can be used to increase the time of the charge collection. But under the circumstance of high radiation fluence rate, due to the serious pulse pile-up of the scintillator detector with the slow decay time, the measured pulse count rate and energy resolution using traditional pulse shaping approach are significantly reduced. In order to overcome this problem, a digital fast shaping algorithm was presented based on the digital deconvolution in this paper. This algorithm can remove the current tails of the scintillator detectors with the slow decay time to obtain an ideal impulse current. Then a narrow pulse can be obtained through pulse shaping, which can thoroughly eliminate the influence of the ballistic deficit. Through the measurement of the ¹³⁷Cs gamma source, when the shaping time is 1.5 μs, the energy spectrum measurement system using the traditional pulse shaping algorithm yields a 6.99% energy resolution of the photoelectric peak and count rate of 68 000 s^-1. While the digital fast shaping system yields a 6.37% energy resolution and count rate of 102 000 s^-1 at the same condition. Thus, the digital fast shaping algorithm can effectively restore deformation and tail of the narrow pulse shaping under the circumstance of high radiation fluence rate, which can improve the pile-up discrimination ability.