The surface characteristic of the heat transfer channel of micro heat exchangers has a significant effect on the flow boiling performance of fluid.Solid surface energy is often used to describe the surface characteristics of the heat transfer channel,which can provide a theoretical basis for the research of the flow boiling performance of the fluid in micro-channels.In the investigation,the contact angles of deionized water,ethylene glycol and formamide with the left,right and bottom surfaces of the heat transfer channel were measured respectively,and the solid surface energy of the heat transfer channel was calculated on the basis of Young's theory.Then,the forming mechanism of the contact angle difference between the inside and outside surfaces of the micro-channels was analyzed through the Wenzel model of droplet.The results show that the solid surface energy of the left,right and bottom surfaces of the heat transfer channel are respectively 5.2,5.6 and 8.2MJ /m²,and the surface roughness difference causes the inside surface features to be different.