Abstract: The formula of detection probability (Pd) of Chi-Square fluctuating targets in a rank binary integration detector is derived. The ealculation shows that asymptotic performance for the model targets is equal with asymptotic performance which is given in [1].Representative numberieal results are included to indicate Pd, which are computed by digital computer DJS-6. The optimal rank quantization is approximataly between 0.8(N + 1) and 0.9(N + 1) for N = 10, 16, 24; M = 16, 24; where N is the number of reference cells, M is the number of radar's pulse repetition rate.