The invention discloses a preparation method of IN718 alloy spherical powder. The method comprises the following steps of step 1, smelting an IN718 alloy master ingot; step 2, processing the IN718 alloy master ingot into an IN718 alloy electrode bar with the diameter of 50 to 90mm and the length of 600 to 800mm, wherein the straightness of the electrode bar is controlled to be smaller than or equal to 0.1mm / m; step 3, placing the IN718 alloy electrode bar in a sealed furnace chamber protected by inert gas, rotating the IN718 alloy electrode bar at high speed, and heating the end part of the electrode bar by using a plasma gun to melt the electrode bar; step 4, atomizing the melted metal under the action of centrifugal force to enable melted metal to fly to form fine liquid droplets, wherein the liquid droplets are quickly cooled in inert gas to form spherical particles, and the spherical particles fall into a collector at the bottom of the furnace chamber to form the IN718 alloy spherical powder; step 5, under the protection of the inert gas, performing electrostatic separation processing on the prepared IN718 alloy spherical powder to remove non-metal impurities from the powder to obtain the pure IN718 alloy spherical powder. The method has the characteristics of good sphericity degree, fine particle size, low oxygen content and few impurities.