Abstract: Due to the indeterminacy of inversion and multimodal of object function, a niching genetic algorithm is introduced in this paper and the adaptive control of probability of crossover and mutation is used. Several local peaks or several global peaks of the object function are found first, the satisfied solution is obtained based on prior information accordingly. The genetic algorithm has been used in interval velocity and thickness inversion of seismic data in detecting the structure of a dykes. Comparing the practical velocity and thickness with the inversion velocity and thickness, the efficiency of multimodal optimization is validated.