The invention discloses an A2B7 nickel hydrogen battery cathode material and a preparation method thereof. The A2B7 nickel hydrogen battery cathode material comprises the following components: LaxSmyMg2-x-yNizAl7-z, wherein the x is greater than or equal to 0.30 and is less than or equal to 1.10, the y is greater than or equal to 0.70 and is less than or equal to 1.50, and the z is greater than or equal to 5.78 and is less than or equal to 7.47. The preparation method provided by the invention comprises the following steps of: carrying out induction melting on lanthanum, samarium, nickel, magnesium and aluminum according to molar ratio of (3.60-11.33) to (7.33-15.49) to (70.86-76.70) to (1.51 to 3.87) to (1.36-5.58) at 1050-1350 DEG C, annealing for 2-8h under 800 DEG C-950 DEG C so as to obtain a cathode alloy material, namely LaxSmyMg2-x-yNizAl7-z without Co, Pr and Nd. The grain of the LaxSmyMg2-x-yNizAl7-z is small, the A2B7 phase content is more than 90%, the components are uniformly distributed, the capacity is high, and the cycling service life is long.