In this study, buckwheat flour was used as raw material to analyze the effect of extrusion cooking on its room temperature viscosity and gel properties. The molecular weight distribution of starch was analyzed by size exclusion chromatography, and the mechanism of pregelatinizing to improve the gel properties of buckwheat flour was discussed. Finally, based on the texture evaluation method of dough sheet, the proportion of pregelatinized buckwheat flour in 50% buckwheat noodles was optimized. The results showed that the buckwheat flour can form a gel in cold water without heating after extrusion cooking, and the viscosity of pregelatinized powder significantly increased at room temperature. The pregelatinized buckwheat flour has the most amylopectin chain length of DP 6~50 and the strongest gel strength，under the processing conditions of a main zone temperature of 200 ℃, a moisture content of 18%, and a screw speed of 220 r/min. When the amount of pregelatinized buckwheat flour was 10%, the dough sheet was the excellent in tensile strength with acceptable adhesiveness. In summary,the specific amylopectin chain length of DP 6~50 in pregelatinized starch was positively correlated with the gel strength of pregelatinized buckwheat flour. Adding an appropriate amount of pregelatinized powder to 50% buckwheat noodles can significantly improve the processing performance of noodles.