Objective To discuss the HBsAg applicable diluent and optimization dilution multiple with i2000 Chemoluminescence Analyzer and provide evidence for diagnosis and therapy of HBV infection.Methods(1) The choice of dilution multiple: The optimization dilution multiple was determined by analyzing statistically frequency of different dilution multiple from 1 192 results which were detected with dilution method suggested by manufacturer in our Clinical Laboratory.(2) The choice of applicable diluent: 30 distinct patient serum(HBsAg250 IU/mL)were detected after 50,100,500 fold dilution with manufacturer diluent,mixture negative serum,normal sodium and 10% calf serum.The suitable diluent and dilution multiple were determined by analyzing statistically test results of manufacturer diluent,mixture negative serum,normal sodium and 10% calf serum.Results(1) In 1 192 diluted samples,95% of the test results were within 50 fold dilution range;98% of the test results were in 100 fold dilution range;99% of the test results were in the range of 500 fold dilution range.(2)There were no significantly different between the detection results of manufacturer diluent and those of mixture negative serum,normal sodium and 10% calf serum.(P0.05)Conclusion When HBsAg250 IU/mL,100 fold dilution is selected firstly.As HBsAg250 IU/mL after 100 fold dilution,500 fold dilution is selected and detected.The manufacturer diluent,mixture negative serum,normal sodium and 10% calf serum are as applicable diluent.