A lownoise and wideband amplifier was designed for the weak laser echo signal. We chose the CFB differential operational amplifier THS4509 with low noise and high bandwidth as the core component; a twostage amplification circuit was adopted in order to obtain a larger gain, and a transmissionline voltage transformer was used to change the output signal from doubleended to signalended. To reduce the noise, we used a lowpass elliptic filter with the best transition zone features to filter out the noise outside the band. The experiences demonstrated that the amplifier had the characteristics of 40 dB gain, 120 MHz bandwidth, and its noise was less than 10mV(pp). It could effectively amplify the weak laser echo signal reflected by the different target objects even with a variety of reflectivity. Furthermore, the amplifier with the above characteristics performed better in solving the problem of long distance and low reflectivity, and its maximum measuring rang can reach 450m proved by actual tests