By studying the numerical calculation of the stochastic-dynamics equation of the laser-DNA interaction,it was found that with the approximation of small signal and adiabatic hypothesis and under suitable conditions,the stochastic chaos will occur in the laser-DNA interactive system. The appearance of stochastic chaos is related to the intensity of laser. When it is very weak there is no chaos and this suggests that small intensity of laser does not make DNA mutate. When laser intensity reaches a certain value,chaos appears and makes DNA mutate. With the increase of laser intensity,the characteristic of chaos in the evolution process of system becomes more and more significant. However,laser intensity can not be too strong,otherwise it will cause very complex chaos that makes a severe problem of uncertainty in laser breeding and brings uncontrollable results instead of inducing DNA to mutate. The influence of the periodical change of environment on laser-DNA interactive system was discussed,too.