Based on the pulse compression characteristics in the nonlinear optical loop mirror (NOLM), the effect of NOLM on a cascad stimulated Brillouin scattering based slow light system is analyzed. In this paper, a ring structure is adopted to simulate the cascad system, so the complexity of system is reduced effectively, and the delay characteristics for various numbers of cycles and pump powers are studied. Analysis shows that the NOLM can effectively suppress the pulse-broadening in the cascaded slow light system, pump power determines the tendency and the final steady-state value of the broadening factor, and the broadening factor trends to the steady-state value after 4 cycles. Furthermore, zero-broadening can be obtained by optimizing the pump power; the delay time is continuously adjustable and without any limit in theory through changing the pump power and the number of cycles; through augmenting the pump power, the multiple-cascad-induced chirp can be reduced.