Influence of a spiral spin structure on the superconducting (SC) pairing in the most probable active $\gamma$ band of $Sr_2RuO_4$ is studied in the mean field approximation. Such structure with "incommensurate" vector $Q=2\pi(1/3,1/3)$ has been proposed as that which removes the nesting instability in $\alfa, \betta$ bands. The model pairing interaction of adjacent centres is adopted. The mixed singlet and triplet SC order is revealed. The d-wave singlet pairing is accompanied by formation of the p-wave triplet pairs with large total momentum Q and spin projections $\pm 1$ onto axis normal to the spin rotation plane of the spiral structure. Both the superconducting and normal states have a broken time reversal symmetry which might be detected by polarised photoemission.