Abstract
We study the mass neutrino interference phase in Schwarzschild-de Sitter space time along the null trajectory and the geodesic line and obtain the effects of cosmological constant Λ on the neutrino oscillation. Firstly, in the high energy limit, we find that the phase along the geodesic keeps the double of that along the null. Secondly, we calculate the phase on the condition that the cosmological constant, Λ, is a small quantity. The correction of the phase due to Λ is given. Finally, we calculate the proper oscillation length in Schwarzschild-de Sitter space-time, which increases because of the existence of Λ, compared with the result in Schwarzschild space-time. All of our results can be reduced to those in Schwarzschild space-time as Λ approaches to zero.