Based on Hertz contact deformation theory, the load distribution of roller and bearing load can be obtained with the consideration of rotating speed and TRB clearance. Furthermore, The TRB load model were introduced into the established dynamic model of helical gear system which includes time varying meshing stiffness(TVMS) of helical gear pair, comprehensive transmission error, gear backlash and bearing mounting style. Dynamic differential equations were solved by Runge–Kutta method. The effect of rotating speed, TRB clearance on the bearing load and dynamic behavior of system were investigated. Results show that input rotating speed and TRB clearance have significant influence on the gear system dynamic behavior. The increase of rotating speed could bring the system into nT-periodic motion, chaotic motion, nT-periodic motion, quasi-periodic motion and chaotic motion. And with the increase of TRB clearance, the system undergoes nT-periodic motion, quasi-periodic motion, and chaotic motion. When the rotating speed is 1000 r/min ~ 2700 r/min, 3200 r/min ~ 4900 r/min or the TRB clearance is less than 5 mm, the system is in nT-periodic motion. When the rotating speed is 4900 r/min ~ 6000 r/min or the TRB clearance is between 5 and 10 mm, the system displays quasi-periodic motion form. When the rotating speed is 2700 r/min ~ 3200 r/min or bigger than 6000 r/min or the bearing clearance exceeds 10 mm, the system is in chaotic motion.