Abstract: OBJECTIVE To establish an HPLC method for determination of the related substances in codeine phosphate. METHODS The test was based on an octadecylsilyl silica gel column; the mobile phase A consisted of 0.2% potassium dihydrogen phosphate and 1% sodium heptanesulfonate (pH was adjusted to 3.2±0.2 with phosphoric acid)-methanol(7:3), the mobile phase B consisted of mobile phase A and acetonitrile(6:4), with gradient elution at the flow rate of 1.0 mL·min^-1; the detection wavelength was 245 nm; the column temperature was 40℃. RESULTS The separation between the main component of the method and each impurity(A-K) were >1.5. The calibration curves of codeine and known impurities were linear in the self-concentration range; and the average recovery rates(n=9) were in the range of 96.7%-103.8% while RSDs were in th range of 1.4%-6.0%. CONCLUSION The method is improved with good specificity and linearity. The self-control method for proposed main component with correction factors is suitable for the quality control of this drug.