By using the linear approximation method, the intensity correlation function C(t) of loss model laser system with a biased amplitude modulation was calculated. The different forms (irregularly periodic increasing, decreasing and so on) were obtained in the evolution of the intensity correlation function C(t) with the time t. The results indicate that: in the case of a0=0.1, the flat irregularly periodic oscillation is shown; the period of irregularly periodic oscillation is adjusted by the low frequency Ω of modulation signal; the initial value and the period of C(t) can be changed by the intensity of quantum noise Q and the high frequency ω of carrier signal.