Based on wavelet transformation and chaos theory, low frequency noise in semiconductor laser is studied. The feasibility of chaotic noise model is discussed and prescribed in detail based on techniques of phase locus, power spectrum，Lyapunov exponents and correlation dimension. And the reasons for this chaos phenomenon it also explained in theory. The rigorous chaotic character of low-frequency noise in semiconductor laser is found, which loys a theoretical basis for the correlative investigation based on semiconductor laser reliability.