The chaotic behaviors of a particle in a triple potential well possessing both homoclinic and heteroclinic orbits under harmonic and Gaussian white noise excitations were studied. Following the Melnikov theory,the conditions for the existence of transverse intersection on the surface of homoclinic or heteroclinic orbits for the triple potential well case were derived, and were complemented by the numerical simulations,from which we showed the bifurcation surfaces and the fractality of the basins of attraction. The results revealed that the threshold amplitude of harmonic excitation for onset of chaos moved downwards as the noise intensity increasesd, which was further verified by the top Lyapunov exponents of the original system. Thus the larger the noise intensity,the more possible chaotic domain in the parameter space.Moreover,the effect of noise on Poincare maps was also investigated.