Aiming at the problem of very-high-cycle-fatigue(VHCF) of aeroengine compressor blades under complex loading, three-point bending ultrasonic fatigue tests of TC4 titanium alloy under stress ratio R of 0.3 and 0.5 were performed, and failure mechanisms of VHCF under three-point bending was also investigated. Test results show that S-N curves present a bilinear characteristic. SEM analysis indicates, the crack initiation sites are transferred from the surface to the sub-surface with the decrease of the maximum stress. Fatigue crack initiations are results of competition between surface slip and internal cleavage fracture. Then a model based on fatigue life is proposed to describe the competition between the two mechanisms, which is in agreement with the experimental results. The temperature of the specimen surface is monitored by infrared camera. It can be divided into four stages in high-cycle-fatigue (HCF) regime: steady rising, steady decreasing, fast rising and fast decreasing stage. While it can be divided into three stages in VHVF regime: steady rising, fast rising and decreasing stage. Finally, The characteristics of heat production and transfer are described, and the correlation between temperature and stress distribution is analyzed.