Field plot experiments were conducted to study the effects of biochar on soil physi-chemical properties, heavy metal passivation and enzyme activities in the red paddy soil polluted by heavy metals. Biochar was added in different amounts of 0, 10, 20, 30 and 40 t/hm², respectively. The soil samples were collected from 0-17 and 17-29 cm soil layers. The soil integrated fertility index (IFI) was used to assess the soil fertility. The results showed that biochar could increase soil fertility by reducing soil bulk density and improving soil porosity, saturated water content, pH, cation exchange capacity (CEC) and the content of soil organic matter (SOM), the available phosphorus, ammonium nitrogen, total nitrogen and dissolved organic carbon (DOC). Meanwhile, biochar could improve activity of soil urease, catalase and urease. The content of available Cd and Pb in soil decreased with the increasing of biochar application amount, whereas the available As content increased first and then decreased with the increasing of biochar amount. The content of available Cd, As and Pb were all minimum when the biochar application was 40 t/hm². According to the evaluation of soil quality by IFI, the order of soil fertility composite quality was followed A30 > A40 > A20 > A10 > CK, the corresponding soil fertility composite quality indexes were 0.64, 0.62, 0.57, 0.47, 0.44, respectively. The evaluation results suggested that the optimal amount of biochar was 30 t/hm² for improving the red paddy soil fertility. In conclusion, appropriate amount of biochar application could remedied the red peddy soil polluted by heavy metal and enhance soil fertility.