The invention relates to the field of motor rotor assembly. The invention discloses an automatic shaft pressing device. A shaft storage tank horizontally stores shafts. A shaft jacking mechanism horizontally jacks shafts on the shaft storage tank one by one. An upper shaft auxiliary mechanism reverses the shafts 90 degrees to a vertical state. An upper shaft hand clamps the vertical shafts. An upper shaft mechanism moves through an upper shaft horizontal shifter and an upper shaft vertical shifter to place the shafts into iron cores. An indexing device rotates the shafts and the iron cores to a next process indexing position. A press driver drives a shaft presser to sleeve the top of the shafts and press the shafts into the iron cores. The upper shaft hand is provided with a second V-shaped groove in the shaft clamping face, so that the upper shaft hand stably clamps the shafts. Hand-free shaft pressing is realized. The automatic shaft pressing device has the advantages of fast production takt, high production efficiency and low production cost.