This paper analyzes the signals impairment in the semiconductor optical amplifier (SOA) based optical buffer for optical packets switching networks, including the shape distortion of single pulse and the pattern dependent distortion of the continuous bit stream due to the SOAs nonlinearity and the limitation of its carrier lifetime, the deterioration of signal-to-noise ratio caused by the accumulation of amplified spontaneous emmision noise of the SOA, and the power leakage. The theoretical analysis and experimental results indicate that the buffered circle is restricted to 20—30, as determined by the signals impairment when a negative control optical pulse with high power is injected into SOA.