Based on the all-fiber ring-cavity multi-pass pulse amplifier, pulses of Q-switched with a few hundred nanosecond duration and repetition rate of 10~50 kHz range are amplified. Although the number of pass is not controlled, some important phenomena such as characteristics of gain and time domain evaluation in multi-pass amplification are acquired, and the output frequency of pulse is changed by the ring-cavity multi-pass amplifier. A gain of 7 dB higher than that of single pass amplification is obtained. Experimental results demonstrate that signal gain and conversion efficiency can be greatly enhanced by using ring cavity multi-pass amplification for a pulse repetition rate of 10 kHz or lower than that. The results can be helpful to investigation on all-fiber regenerative amplifier.