The effects of the microsecond pulse-width stray light on the shock wave induced by the nanosecond pulse-width of master laser are studied. By adjusting the half-wave voltage loaded on the Q-crystal, the energy of the stray light can be changed. Meanwhile, the shock wave induced by the master laser would be measured by polyvinylidene fluoride (PVDF) under the condition of the unchanged pump power. The result indicates that with the increase of the energy of the stray light, the energy of the master laser decreases and the pulse width of it increases, so the power density of the master laser and the peak pressure induced by the master laser would decrease; in addition, when the whole laser energy is 6.5 J and the energy of the stray light is 2280 mJ, the aluminium foil is ablated thoroughly. According to the experimental result, the formula of the peak pressure induced by the laser has been revised, which can be applicable to the computation of the peak pressure induced by the master laser under the condition of the stray light.