Adjoint Monte Carlo Method possess especial superiority for cal-oulating the point flux or radiation environment problem, while the other methods do not possess so far. However, the variance of adjoint Monte carlo method is always large.In this paper we present a new method with reduced variance for multigroup adjoint intergral equation of neutron flux, Namely the method of "the best" changed factor of weight, The calculations show that this method can reduce the variance remarkably.