The objective of this long-term positioning experiment was to study the effects of biochar addition on soil physicochemical properties, heavy metal concentrations and microbial biomass in the red paddy soil polluted by heavy metals. Biochar was added once at rates of 0, 10, 20, 30, and 40 t/hm², and the topsoil samples (0-15 cm) were collected in September 2017. The results showed that biochar addition had signification effects on soil physicochemical properties, heavy metal concentrations and microbial biomass. Soil pH, electrical conductivity (EC) and soil organic matter (SOM) were observed significantly increased under biochar addition as compared to the control, ranging from 5.11% to 18.43%, 37.62% to 104.31%, and 1.72% to 22.41%, respectively. However, the available phosphorus and ammonium nitrogen content were firstly increased and then decreased with the biochar addition rate increment, and the highest available phosphorus and ammonium nitrogen content were in the 10 t/hm² and 30 t/hm² treatments, respectively. As for the changes of heavy metals, the available content of Cd and Pb decreased with the biochar addition rate increment, whereas the available content of As increased firstly, and then decreased with biochar amendment rate increased, and the highest content of As was in the 40 t/hm² treatment. Soil microbial biomass carbon, nitrogen and microbial quotient firstly increased and then decreased with the addition rate of biochar increment, they maximum value of them were all in the 20 t/hm² treatments. Correlation analysis showed that the biochar addition was significant negative correlated with the available content of Cd and Pb (P<0.01). The path analysis indicated that the available content of Cd in soil was mainly affected by biochar addition through the direct impact, whereas the soil pH, EC, SOM, microbial biomass carbon, nitrogen, and available phosphorus content could mainly affected the available Cd content by indirect impact. In conclusion, biochar addition can not only improve status of soil heavy metal pollution and soil physicochemical properties, but also improve the soil biological properties. This study can provide a scientific basis and support for improving the soil fertility and remediating the heavy metal contamination.