Energy is concentrated in the middle part of the beam for the traditional narrowband laser beam shaping. This energy distribution approximates a Gaussian distribution which can not meet the requirements of large field line Pushbroom 3D imaging laser radar technology. A novel beam shaping technology is proposed to solve the problem of Pushbroom lidar which needs a narrow strip of the laser beam. According to the optical properties of cone mirror, we use Biaxial Axicon to change the spatial energy distribution of the laser beam, and then energy distribution of the laser beam are shaped "U" through the cylindrical lens. Experimental results show that the "U" shaped narrowband of the laser beam can meet the requirements of large field of linear array push-broom imaging 3D laser radar.