By adding different content of trace Bi and adjusting the content of residual rare earth, the effect on the microstructure, tensile strength, elongation, hardness and -40 ℃ low temperature impact toughness was studied. The results showed that, for 180 mm ×180 mm×200 mm specimen, adding 0.012% Bi could obviously eliminate the chunky graphite. But for 250 mm×250 mm×300 mm test block, adding trace Bi could only inhibit chunky graphite to a certain extent. With the increased amount of Bi, the inhibition of chunky graphite enhanced at first and then weakened, with the best value between 0.010% and 0.012%. Meanwhile, the value of tensile strength, elongation and -40 ℃ low temperature impact toughness was 337 MPa, 10.4% and 10.5 J, respectively. Reducing the content of RE and making wRE /wBiadd =1.3~1.5 could further reduce the chunky graphite and improve the comprehensive mechanical properties.