Recently problems requiring control unmanned underwater vehicles (UUV) at large angles of inclination (pitch and roll), become more frequent. Traditional attitude control systems use Euler angles. However, the performance of traditional systems decreases with the increasing of the tilt angles, which delays their use for new tasks. To solve this problem, stability analysis of the UUV’s attitude control system according to the generalized Nyquist stability criterion is carried out. The analyses showed that the stability of the system depends on the UUV inclination along the roll. However, at large angles of inclination, the roll channel is subject to perturbations from the yaw and pitch channels. The roll control system synthesis is solved as the Н∞ - optimization problem with the requirements of low sensitivity to perturbations from other channels. The simulation results on the full non-linear UUV Aqua-MO model confirmed the efficiency of the approach in question and demonstrated the best quality in comparison with PD controller. The obtained stability condition and synthesis approach allow to expand the working angles and improve the quality of the existing UUV control systems. These results are useful for the development of new systems as well.