Abstract: This paper uses the Quadratic/Linear Traveltime Interpolation (QLTI) ray tracing method to get the traveltime of the headwave including direct wave, reflection wave, and refraction wave. This kind of seismic ray tracing algorithm (QLTI) is more precise and suitable in the research of inversion. The Niche Genetic Algorithm is introduced for the indeterminacy of inversion. Every individual in every population uses the QLTI method to get the traveltime. Through the object function controlling the crossover probabilities and the mutation probabilities, the Niche Genetic Algorithm can get the best velocity distributing tomography of the media. Inversion results indicate that this method can deal with complex media, and the results are steady and credible.