Abstract: The paper describes the signal processing method of the digital fuel ball counting system designed for the 10 MW high temperature gascooled test reactor (HTR10). The signal peak is searched by the relative amplitude instead of the absolute level, so as to reach high accuracy and speed. The special filtering algorithm not only can accelerate the searching speed for the signal peaks, but also can eliminate the random disturbance,and identify adaptively the reference level when no ball is passing. Furthermore, the realtime acquisition and online processing of the signals from the multiple counters are carried out parallelly and simultaneously.