The influences of noise on chaotic dynamics in a vibro-impact oscillator, modeled as Duffing Van der Pol (DVP) system with unilateral rigid barrier, are investigated. An interpolation strategy is introduced to locate the impact instants, and effective numerical method is proposed to improve the computational precision in the vibro-impact oscillator. Near the boundary crisis, the phenomenon of noise-induced chaotic transition occurs. Our studies reveal that the escape of oscillator from the boundary is responsible for this chaotic transition. The increase of noise can aggravate this escape.