Theinertiasofthefluidandtheinnercylinderincoaxialcylinderrheometer(CACR)havegreatinfluenceontheunsteadyflowofnon-Newtonianfluid.EvenfortheNewtonianfluidthereexistthesocalled'stressovershoot'phenomenon.Inthepresentarticlethisphenomenonwasstudiedindetailandamethodcorrectingthemeasuredresultsforanunsteadyflowintherheometerwasproposed.Itisfoundthattheinertiaeffectofthefluidcanbeignoredwhenthegapbetweencylindersissmall.