In order to realize the monitoring of crop growth and combine with the development trend of fluorescent lidar technology, a set of fluorescent lidar system suitable for crop monitoring is built by using laser induced fluorescence technology in this paper. In order to improve the stability of the system and simplify the structure of the system, the laser transmitting system and the receiving optical system are combined into one. By adjusting the negative lens to the position of the cassegrain system, the laser transmitting and signal receiving of distant objects can be carried out. At the same time, in order to improve the stability of the system, a coaxial correction method and device of the lidar system are proposed. By adding a two-dimensional adjustable stop matching the field of view to the receiving optical system, the focal length adjustment problem is realized in the scene of distance change, and the detection ability of the received target signal is enhanced. In this study, the whole fluorescence lidar system was constructed and coaxial installation was carried out, and the fluorescence spectra of the blades were measured and verified. The main fluorescence characteristic peaks of the blades were detected at 80 m,100 m and 150 m respectively. The experiment proves that the fluorescence signal obtained by coaxial adjustment is of good quality and the system is stable. After the crop distance changes, the high SNR fluorescence measurement of samples at different distances can be directly realized by adjusting the system, which provides theoretical and technical support for the fluorescence lidar system in agricultural crop detection.