The present invention discloses a preparation method of instant bone milk, including: washing edible animal bones and then crushing, adding a certain amount composite effect enhancer, performing two high pressure hydrolysis-instantaneous pressure relief in high pressure hydrolysis chamber, collecting liquid-phase materials, performing centrifugation for degreasing, wet sieving, homogenizing, spray drying to obtain powdered instant bone milk. A device for preparation method of instant bone milk comprises a high-pressure hydrolysis tank, a grading conveying pipe and a gas-liquid separator. The instant bone milk prepared by the present invention has stable chemical structure, uniform particle size distribution and regular normal distribution, high protein solubility and good solution stability. And the preparation method has simple process, low cost equipment and good versatility.