“Hot Green No. 2” pakchoi was pot-planted with five treatments including 0% C,1% C,2% C,4% C and normal application of potassium fertilizer to investigate the effects of biochar application on potassium content of different forms in red soil and the growth of pakchoi. Results showed that the effects of biochar on content of water-soluble potassium,exchangeable potassium and non-exchangeable potassium in red soil were increased by 12.6%-51.8%,13.3%-43.5% and 10.3%-26.1%,respectively,compared to the control. The effect of biochar on improving different forms of potassium between 4% C and normal potassium was the most similar. Biochar application increased soil pH value significantly by 0.06-0.25 units,as available phosphorus,available potassium and organic carbon in soil. Also the cation exchange capacity,exchangeable calcium and magnesium content increased significantly,while the exchangeable aluminum content decreased significantly with a decrease of 87%-98%. Biochar application could improve pakchoi growth performance as increasing the biomass,leaf number,plant height and fresh weight of pakchoi.