Abstract The common buckwheat ‘cv. Fengtian 1’ (FT1), ‘cv. Yuqiao 4’ (YQ4), ‘cv. Dingtian 2 (DT2)’, and ‘cv. Tongliao (TL)’ were selected to investigate the characteristics of starch synthesis and grain filling. The chlorophyll and chlorophyll a / b contents of leaves in the third stem showed a steady downward trend with the growth of common buckwheat. Whereas, FT1, YQ4 and DT2 showed higher chlorophyll content than that of TL at 7d and 14d. The activity of soluble starch synthase(SSS) and adenosine diphosphate glucose pyrophosphorylase (ADPGP) in the four tested varieties showed a rapid upward trend until 14 days after heading but then rapidly decreased until 21 days after heading. The average adenosine diphosphate glucose pyrophosphorylase activities of FT1, YQ4 and DT2 were higher than TL, while the average soluble starch synthase activities were similar among the four tested varieties. Consistently, the four tested varieties showed rapid accumulation of starch, amylose, and amylopectin during the prefilling stage, but no difference of starch content was found at maturity. The filling process of the four common buckwheat varieties exhibited an “S” curve. The Richards equation was utilized to evaluate the grain-filling process of common buckwheat. YQ4 showed the largest values of initial growth power ( R 0 ). The time reaching the maximum grain-filling rate ( t max.G ) of FT1 was the longest, and the maximum grain-filling rate ( G max ) of DT2 was the fastest.