We propose a generalized Ising spin model, which contains the pure Ising model, the mixed spin model proposed by Schofield and Bowers and the particular site-diluted Ising spin model as special oases. A real space renormalisation group is applied to this model, the phase diagram is found to have three nontrivial fixed points (a Ising, a tric-ritical and a first order phase transition point). And it is demonstrated that mixed spin model and pure Ising spin model belong to the same universality, which is in agreement with the conclusion made by Schofield and Bowers who calculated the critical exponents of mixed model directly.