Abstract: Circular pin fins are commonly used in the internal cooling channel of the turbine blade. This paper mainly investigated experimentally the flow mechanism driving heat transfer enhancement in a wide channel with staggered circular pin fins. The flow field in the mid-plane of the channel was measured using Particle Image Velocimetry (PIV). Nusselt number distributions on the endwall was obtained by means of Thermochromic Liquid Crystal (TLC) in the same geometry under the same Reynolds number (1.0×10⁴ or 2.0×10⁴). Results indicate that downstream of circular pins the distribution of v_rms is similar to that of Nu. However, when the flow is developed, smaller scale fluctuation increases, and the distributions of turbulent kinetic energy (K_t) and Nu are more uniform. The heat transfer enhancement and cross-stream velocity fluctuation are decreased when Re increases. It is concluded that intense lateral velocity fluctuation induced by vortex shedding is the main flow mechanism driving local heat transfer enhancement. Small scale fluctuation makes local heat transfer uniform.