A kind of circuit characterized by sampling, amplifying and adjusting light pulse was introduced. It can be applied to the real-time monitoring of narrow light pulse. Theoretically, the paper analyses the relationship between the pulse slewing rate and the selection of an amplifier, also the relationship between the bandwidth of the retainer and the selection of a hold-capacitance is deduced. The main performance of the peak holder is analyzed and the method of selecting amplifier and holding-capacitance is introduced. According to the theoretical analysis, high-speed, weak light-pulse signal sampling and peak-holding circuit is designed. PIN diode connected a 50 ohm resistor is used to convert electric current to voltage. The AD8009 voltage amplifier brings about amplifying voltage from 1V to 3V. Sampling and broadening peak can be achieved by OPA615. The excellent EP2C5T144 in the control field is qualified to provide a control signal, which is able to control the conversion of peak sampling or holding. Therefore, the amplification and broadening of narrow pulse signal are obtained. This light power signal pulse width is 100 ns, with 50 ns rising time and 50 ns falling time. Light power signal varies from 0.1w to 1w. The current signal from PIN diode is 1~10 mill ampere (mA). This circuit is effective for the signal of 100 ns pulse width and 50 ns rising time. It is proved that the scheme is feasible and this circuit-design can be used in practical application.