Na3Zr2-x InxSi2-xP1+xO12 system has been investigated by means of solid state reaction, X-ray powder diffraction technique, microscopic observation, specific heat measurement and complex impedance measurement. There are two kinds of solid solutions in this system: monoclinic solid solution (0≤x3Zr2-xInxSi2-xP1+xO12 solid solution, which begins at the composition of x=0.8, has been stabilized at room temperature. The stabilized materials do not exhibit any phase transformation in the heating process. The electrical conductivities in Na3Zr2-xMxSi2-x P1+x O12 (M = Y, Yb and In) systems have been compared, and discussed from the point of view of crystal chemistry.