Due to the absorption and scattering of water, the beam energy will attenuate in the process of propagation, and the laser pulse will be widened, which restricts the detection range and accuracy of underwater lidar. Based on the application background of underwater weak and small target detection in turbid water environment, this paper establishes the Monte Carlo simulation model of underwater photon propagation, simulates the backscattering echo signal of water body with different attenuation coefficients and scattering rates, and analyzes the variation trend of the corresponding backscattering echo signal of water body. The simulation results show that the number of photons received by the laser echo signal of near-field water body gradually increases with the increase of attenuation coefficient of water body; With the increase of water scattering rate, the photon extinction speed of echo signal gradually decreases. The lidar echo signal test experiments under different turbidity are carried out. The experimental results show that with the increase of water attenuation coefficient, the laser backscattering echo amplitude of water gradually increases and the pulse width gradually widens. When detecting dim and small underwater targets in turbid water, with the increase of attenuation coefficient of water, the difference between water echo and target echo should be enhanced by gradually reducing laser energy or receiving system gain, so as to improve the signal-to-noise ratio of dim and small underwater targets in turbid water. The experimental results verify the theory and simulation results, and provide theoretical support for the laser energy selection and the gain design of the receiving system of the underwater weak and small target laser detection system under different water qualities in the turbid water environment.