In order to optimize the axial irradiation uniformity of a laser in plasma, this paper investigates the role played by the compound lens using a ray-tracing method. Obtained results show that the adoption of the compound lens is capable of increasing the axial line-focus length. Meanwhile, after the energy attenuation in the plasma has been considered,moderating the optical parameter of the compound lens to obtain the corresponding energy output to compensate for the attenuation optimizes the irradiation uniformity along the focal line.