In order to improve the accuracy in thyroid tumor detection, the selection, crossover and mutation operation of genetic idea was introduced into the bat algorithm and a novel registration method of SPECT image and B-type ultrasound image was proposed based on genetic idea bat algorithm. First, according to the common contour characteristic of thyroid and tumor, improved gradient normalized mutual information was used for similarity measurement. Second, the genetic idea bat algorithm was used to optimize the space registration transform parameters. The experimental results show that improved gradient normalized mutual information has high locating accuracy of registration and less local extremum, genetic idea bat algorithm improves the rate and accuracy of convergence of registration. The method achieves desired effect in registration of SPECT image and B-type ultrasound image.