Abstract: This paper introduces an improved technology for spectrum stabilization of NaI(Tl) gamma spectrum. This technology is based on the system using a reference peak, which is equivalent gamma peak of ~(241)Am source. The computer seeks peak’s (position) deviation and computes adjust value of programmable amplifier and controls (programmable) amplifier to stabilize spectrum by digital PID. This is a technology of (spectrum) stabilizing with “hardware+reference-peak+software” and has high stability and fast speed of spectrum stabilizing.