In this paper, homoclinic bifurcations and chaos in a double well Duffing vibro-impact oscillator under harmonic and bounded noise excitations are investigated.Melnikov's method in the deterministic vibro-impact system is extended to the analysis of homoclinic bifurcations and chaos in the stochastic case.The analytic conditions for occurrence of chaos are derived by using the stochastic Melnikov process in the mean-square-value sense.In addition, the numerical simulations confirm the validity of analytic results.Also, the influence of some system parameters on the threshold of chaos is studied.