The research on the influence of the dynamic positioning capability of semi-submersible unit under different environmental direction combinations is carried out. Through the combination of different environmental directions, the thrust utilization curve is calculated under specified environmental conditions, and the maximum and minimum thruster utilization rates are obtained. It is found that it is not the worst case of dynamic positioning capability when the wind, wave and current are collinear. The environmental load is greater and the thruster utilization coefficient is higher, when the wind and current have a certain angle with the wave. During the actual unit operation, the wind, wave and current are non-collinear, especially when the environmental conditions are severe; it needs to adjust unit heading to ensure the safe operation of the unit.