Abstract: To slove the heat transfer problem of electronic chips,this paper studied the fluid flow and heat transfer condition when deionized water flew through the microchannel heat sink. The heat sink was welded by cooper and the microchannel had a hydraulic diameter of 0. 23 mm. The heating flux was 2 × 10⁶W/m² and the Re was between 252 and 1 060.Resultsshow that the periodically changeable crosssections microchannel heat sink with triangular reentrant cavities has a better performance than conventional rectangular microchannel heat sink,and both the heating surface's average temperature and maximum temperature of the former is 2-3 ℃ lower than the later one and the pressure loss difference between the two heat sinks is small; with the increase of the flow rate the heating surface's average temperature is reduced; when the flow rate increases to a appropriate degree,the temperature change will not be obvious,and it suggests that the heat transfer performance cannot be enhanced only by increasing the power of pumps.