The mechanism of superconductivity in A3C6o(A=K, Rb and Cs) appears to be onernof difficult question in the theory of supercond uctivity. In this Work we try to showrnelectronic( exciton) and phonon-exciton combined mechanism of superconductivity inrnA3C60 superconductors.rnIn the first part of our work we try to show exclusively excitonic mechanism can notrnproperly explain superconductivity in A3C6o(A=K, Rb and Cs) superconductors. Asrna result of this and the existence of small isotope effect we try to explain mechanismrnof superconductivity in these compounds by phonon-exciton combined mechanism.rnOur result shows phonon-exciton mechanism is capable of explaining the whole rangernof Tc values for all of these superconductors. The isotope effect and reduced gaprnvalues are in good agreement with the experimental values. Also it is inferred thatrnA3C60 superconductors are BCS type assisted by excitonic effect.rnI