Barium atom is one of candidates for optical atomic clock. Laser cooling and trapping the atom need sufficient spectroscopic information of relevant energy levels. The excited energy level 6s6p3P1 is very important in the experiment of laser cooling and trapping barium atoms. Hanle effect was examined both theoretically and experimentally for the 6s2 1S0 to 6s6p 3P1 transition at 791 nm. A theoretical model was developed to include the influence of linewidth and intensity of probe laser on the fluorescence of Hanle effect. By fitting the experimental measurement with the model, lifetime and transition probabilities of 6s6p 3P1 state to lower states were obtained and found to be in good agreement with other reports.