The invention discloses a gear box additional damping noise reduction method based on modal strain energy, which comprises the following steps: S1, establishing a gear box model, and carrying out modal analysis; S2, calculating a modal damping ratio of each order modal of the gearbox; S3, constructing a gear box boundary element model and a Box sound field, and calculating an acoustic transmissionvector; S4, performing vibration response calculation; S5, obtaining the relationship between the vibration speed and the sound pressure of the field points, superposing the sound pressure level caused by each node of the gearbox to each corresponding field point, and solving the radiation noise of the field points; S6, adding damping to the area corresponding to the field point with the maximumsound pressure level on the gear box, establishing an additional damping gear box model, and solving the radiation noise; and S7, performing noise reduction after additional damping, the scheme is determined to be a gearbox model with additional damping, noise reduction is not carried out after additional damping, and the step S6 is executed again to change the scheme with additional damping. Themethod is good in noise reduction effect on the gear box, good in practicability and worthy of popularization.