The crystal structure, spontaneous polarization, contributions of electrons and phonons to the dielectric and piezoelectric responses of BaTiO3/SrTiO3 (1:1) 10-atom superlattice are calculated using first-principles. We explore the ground structure from the highest P4/mmm phase by successively freezing the unstable polar modes. We find that the ground structure possesses the Cm symmetry. The contributions of phonons to dielectric and piezoelectric tensor coming from individual atoms and individual modes are explored. Detailed analysis shows that the ε22 and e26 are mainly due to the A“phonons with ωλ=197 and 146 cm-1, while the A” phonons with ωλ=97 cm-1 also make relatively large contributions. The ε33 and e33 are mainly due to the A' phonons with ωλ=189 and 139 cm-1. The ε11 and e11 are mainly due to the A' phonons with ωλ=246 cm-1. On the other hand, the O and Ti atoms make great contributions to the lattice dielectric and piezoelectric responses.