Basedonsomerecentresultsforinterlacingeigenvalueintervalsfrom1-parameterfamiliesofsequencesofeigenvalueinequalities,anewmethodisgiventosolvingtheindexproblemforSturm-Liouvilleeigenvaluesforcoupledself-adjointboundaryconditionsintheregularcase.ThekeyisanewcharacteristicprincipleforindicesforSturm-Liouvilleeigenvalues.Thealgorithmcorrespondingonthecharacteristicprinciplearediscussed,andnumericalexamplesarepresentedtoillustratethetheoreticalresultsandshowthatthealgorithmisvalid.