We demonstrate that an average power of 45.5 W at 532 nm is obtained with a 13 mm length K3B6O10Br (KBB) crystal corresponding to a conversion efficiency of 36.5% for the first time. The power stability of the 532 nm output power measurement indicates that the standard deviation jitters of the average power are 1.46% and 1.50% at 24.8 and 43.8 W, respectively. The effective nonlinear optical coefficient deff is also obtained as 0.92 pm/V by the phase-matching (PM) method. The angle and temperature bandwidths of second-harmonic generation (SHG) for 1064 nm pump light are also investigated. Therefore, KBB crystal can be a promising nonlinear optical material for visible laser generation.