The invention discloses a manganese-bismuth-iron-phosphor permanent magnetic alloy plating solution and a preparation method thereof, which belong to the field of metal plating electro-deposition. The manganese-bismuth-iron-phosphor permanent magnetic alloy plating solution contains ferrous chloride, manganese chloride, bismuth chloride, and a proper amount of water, and additionally comprises boric acid, sodium hypophosphate, sodium citrate and ascorbic acid. Each component of the plating solution is, by weight, 35-45 parts of boric acid, 30-45 parts of sodium hypophosphate, 5-15 parts of ferrous chloride, 55-65 parts of manganese chloride, 4-10 parts of bismuth chloride, 35-45 parts of sodium citrate, and 1-5 parts of ascorbic acid. The invention also provides the preparation method of the manganese-bismuth-iron-phosphor permanent magnetic alloy plating solution, and the preparation method comprises: taking a Pt sheet as an anode, taking a workpiece to be plated as a cathode; and carrying out plating in the plating solution, wherein the temperature of the plating solution is 20-40 DEG C and the voltage while plating is 2.0-5.0V. The plating solution is high in chemical stability and low in cost and has no pollution. The preparation method is simple and controllable; a prepared manganese-bismuth-iron-phosphor permanent magnetic alloy plating layer is high in corrosion resistance and good in magnetic performance; and the plating solution is mainly applied to the fields such as surface decoration of hardware products and magnetic materials.