The effect of alloy element Zr on the Nb3Sn growth kinetics at the Cu-Sn/Nb interface has been investigated. Experiments have revealed that the addition of Zr in single core composites increases the growth rate substantially and the variation of the Nb3Sn layer thickness with reaction time obviously exceeds the parabolic law. These results cannot be interpreted fully taking into account the fineness of Nb3Sn grains caused by the ZrO2 particles formed during heat treatment, and it is necessary to consider the increase of diffusion coefficient caused by supersaturation of vaeances around the ZrO2 particles. The depletion of Sn contents in the Cu-Sn matrix of multifilamentary composites during heat treatment greatly influenced the growth rate. The revised formula of growth kinetics gives a satisfactory explanation on the experimental results.