Abstract: Femtosecond Laser can create micro-structures on metal surface by reducing materials methods. The micro-structures on heating surface lead to larger contact area, which could increase the heat-transfer characteristics between surface and the coolant. As a kind of nucleation site, the micro-structures might have advantages on the bubble boiling. There are lots of research on many modified surface in pool boiling conditions, and the results shows that the modified surface with plenty of micro-structures can enhance the two phase heat-transfer parameters. The difference of bubble behavior on the modified surface is also observed. Existing studies indicates that the micro-structures on modified surface have a significant impact on the heat-transfer ability. However, most of researchers studied the heat transfer enhancement in pool boiling environment, resulting in the lack of data in flow boiling environment. Furthermore, the experimental data of modified surface prepared by femtosecond Laser in rectangular channel is in need. As a kind of typical thermal-hydraulic channel, rectangular channel is widely used in heat ex-changer, electronic cooling equipment and so on. Using laser modification method, flow heat transfer can be enhanced without changing the channel structure and macroscopic size. In order to explore the availability of femtosecond laser surface modification technology in heat transfer facilities, the honeycomb micro-structures was prepared by femtosecond laser on the surface of rectangular channel. Single-phase and two-phase heat-transfer experiments were carried out in 2 to 4 MPa environment. The experimental result shows that honeycomb modified surface has the heat-transfer enhancement benefits. In single-phase condition, the increase amplitude of Nusselt number on honeycomb modified surface is not significant. In two-phase condition, the increase amplitude of convective heat transfer coefficient on honeycomb modified surface is over 165%. As the rate of flow decreases, the heat transfer enhancement effect of the modified surface increases. With the increase of boiling number, the heat transfer enhancement effect of the modified surface is also promoted. The comprehensive comparison of experimental results between single-phase data and two-phase data proves that the increase in contact area caused by the micro-structures of the honeycomb surface is not the main reason for the improvement of two-phase heat transfer coefficient. The mechanism of honeycomb modified surface enhancing two-phase heat transfer should be the large number of nucleated voids owing to micro-structures fabricated by femtosecond laser. When the heat flux increases, the boiling phenomenon on the surface becomes more intense, and the surface with more nucleated voids has better characteristics of heat transfer. Experimental result shows that the single-phase friction resistance coefficient caused by the modified surface can be increased by 40.9%. In practical application conditions, it is necessary to balance the negative effect of increased resistance and the positive benefit of enhanced heat transfer.