For the aim of the fiber pump coupling, calculation and experiment are carried out for the fiber 1∶1 spatial coupler composed of two aspherical lens. Optical pathway is analyzed according to the variation regularity of Gaussian beam. According to the poor coherence of the LD output beam, ray tracing calculation is carried out for the optical pathway diagrams of the coupler. It can be found that the coupler constituted with ellipsoid lens is more stable than that with hyperboloid lens in the case of the wavelength changing and so on. The aspherical lens that meets the calculation result is chosen to constitute the coupler. The couplers with transmittance of 95% composed for the experiments demonstrated a coefficient of 90% LD coupling into a length of multimode fiber with core diameter of 200 micro-meter without antireflection coating at the end surface.