In order to deeply understand the heat transfer mechanism of the channel with side-outflow, a transient measurement technique of using narrow-band thermochromic liquid crystal is employed to determine heat transfer characteristics on the inner surfaces of trapezium channel with ejection through the suction holes. Experimental studies are carried out to investigate inner surface Nusselt numbers under various spaces between holes, Reynolds numbers and suction-holes-flow ratios. The result indicates that the increase of space between holes has weak influence on surface average Nusselt numbers, but makes the Nusselt numbers distribute more uniformly and the heat transfer intensity is enhanced with the increase in inlet Reynolds numbers. With the increase of the suction-holes-flow ratio, heat transfer are declined obviously in the same position along the main flow, and the surface average Nusselt number is also declined.