Whether the transitions between 6s5d ³D and 5d6p ³F can be used for laser cooling of barium heavily depends upon the transition probabilities of 5d6p ³F-5d²³F. Taking the transition 6s5d ³D32-5d6p ³F4 as a scale, the leakage rate of 5d6p ³F4-5d²³F was used to evaluate the transition probabilities. 706 nm laser pulses with different durations were applied to a barium atomic beam for 6s5d³D3-5d ^{2 3}F4 optical pumping, and the remaining percentages in 6s5d ³D₃ were measured. After exponential fitting, the transition probability of 5d6p ³F4-5d^{2 3}F_3,4 was determined to be 2.1(4)×10⁴ s^-1, which is in agreement with theoretical calculations using the scaled Thomas–Fermi–Dirac method.