The (La4MgNi17.5Mn1.5) alloys at different melt-spun speeds were prepared by using a vacuum melt-spun furnace, and the phase structure and electrochemical properties of alloys were studied. X-ray diffraction analysis results show that melt-spun La4MgNi17.5Mn1.5 alloys are composed of CeCu5-type, Pr5Co19-type and CeNi2-type phase. As the melt-spun speed increased, the phase abundance of CeCu5-type increased, but that of Pr5Co19-type decreased. Scanning electron microscopy–energy-dispersive spectroscopy analysis results show that melt-spun treatment can refine grain and make the alloys homogenization. Electrochemical tests show that all alloys have good activation performance within four cycles. With the increase in melt-spun speed, the cycle stability (S) of the alloys was improved obviously. After 100 cycles, the retention rate (S100) of the alloy increased from 54.82% (as-cast) to 82.29% (25 m/s). Nevertheless, the maximum discharge capacity (Cmax) and high-rate dischargeability gradually decreased.