Abstract: The experiments of solution culture with different potassium levels and soil culture with deficient potassium were carried out to study the physiological and biochemical characters of grain amaranth(Amaranthus Cruentus L.) with rich-potassium genotypes(RPG). The results showed that the chlorophyll contents and photosynthesis and the contents of proline, free amino acids and soluble sugar of RPG(R104 and K12) were higher than that of M9(common genotype, CG). The activities of POD, SOD and ATPase in grain amaranth were affected by different organs, position of leaf, potassium levels and development stages: The three enzymes activities of RPG were higher than CG, and the activities of SOD and ATPase in leaf were higher than in roots, POD and SOD activities were significantly lower in old leaf than in young leaf. The activities of POD, SOD and ATPase in leaf were increase with the potassium supply and the enzyme activities were reduced with prolonged the growth days.