The crystal structure of the high-pressure phase methane B was investigated. Recently it was observed experimentally that crystal methane experiences a phase transition at high pressure, but the structure itself was not solved. In the present work we study different crystal structures of methane with the different unit cells by using USPEX evolutionary algorithm. Then we compare results with X-ray single-crystal diffraction data. This phase is difficult for experimental determination which leads to the difficulties with interpretation of the experimental data. Knowledge of this structure clarifies the sluggish transition between A and B methane phases.