Based on the effective-mass approximation and variational approach, the ground-state exciton binding energy, the interband emission wavelength, and the radiative lifetime as functions of the quantum dot (QD) sizes (height and radius) and In content in the InxGa1-xN layer are investigated theoretically in strained wurtzite (WZ) ZnSnN2/InxGa1-xN cylindrical QDs, with considering a three-dimensional carrier confinement in QDs and a strong built-in electric field (BEF) effect due to the piezoelectricity and spontaneous polarization. The computations are performed in the case of finite band offset. Numerical results elucidate that the ground-state exciton binding energy decreases with increasing QD sizes and In content when In content x<0.3. As In content increases, the interband emission wavelength has a red-shift if the dot height L<2.2?nm, but the interband emission wavelength has a blue-shift when L>2.2?nm. and it has a red-shift with increasing QD size. In addition, the radiative lifetime increases with increasing QD size and decreases with increasing In content. The built-in electric field decreasing linearly with In content reduces the ground-state exciton binding energy, and increases the interband emission wavelength and the radiative lifetime. Because the electric field in the ZnSnN2 layer exists along the grown direction of the heterostructures, the influence on the luminescent properties from height L is more visible than the influence on the luminescent properties from radius R. So, in the investigation of the luminescent properties, the BEF and the QD height L are important. Furthermore, the ground-state exciton binding energy, the interband emission wavelength, and the radiation lifetime in ZnSnN2/InxGa1-xN QDs are all larger than those in InxGa1-xN/GaN QDs, especially for QDs with low In content.