SrTiO3 doped ceramics of （1-x）（K0.5Na0.5）NbO3-xSrTiO3 （0≤x≤0.15, （1-x）KNN-xST） were prepared using solid state reaction method and the phase components, crystal structure, and dielectric properties were investigated in this work. It is found that all samples （0≤x≤0.15） are single phases with a perovskite structure within the temperature range from 10 to 800 K. The （1-x）KNN-xST compound has the orthorhombic structure when SrTiO3 concentration is below 0.1, while it shows cubic structure when x ≥ 0.1. It changes from the normal ferroelectric phase to ferroelectric relaxors when increasing the SrTiO3 impurity below a certain temperature. The critical temperature of （1-x）KNN-xST decreases dramatically while the FWHM of D and the critical parameter γ increase with increasing SrTiO3. The temperature spectrum of permittivity loss ε″r indicates that the loss duc to relaxor polarization plays the key role at low temperatures, however, the loss duc to current leakage is significant in the region of high temperatures.