A novel automatic transmission that achieves power-on shifting with only one friction clutch, i.e., an overrunning clutch shift-assistant transmission (OCT) is developed for wind turbines. This transmission realizes continuous shifting by alternating power transfer between a friction clutch and an overrunning clutch. To study the shift smoothness of this automatic transmission, a six-degree-of-freedom dynamic model of a two-speed transmission was established. A coordinated control strategy for the clutch and power source during shifting was proposed, and simulation and test bench studies were conducted. The results show that the proposed upshift and downshift control strategies can effectively reduce shift impact, keeping the jerk during shifting within 10 m/s3.