The invention relates to an offshore wind farm grid-connected power transmission system. The system comprises an offshore alternating current circuit breaker platform, the offshore alternating currentcircuit breaker platform comprises two main buses, and at least one group of 3/2 alternating current circuit breakers are connected between the two main buses. Each group of 3/2 alternating current circuit breakers consist of three serial-connected alternating current circuit breakers and two branches, wherein one branch is used for being connected with a corresponding wind farm and the other branch is used for being connected with a corresponding offshore converter station. Fault isolation can be achieved, the normal operation of other systems is ensured, and the flexibility and power supplyreliability of the system are improved. According to the system, the problems of the increase of control complexity caused by direct current faults when multiple VSC-HVDC direct current sides are connected in parallel and the high fault handling cost caused by expensive direct current circuit breakers are avoided, and the problem that the direct current faults are difficult to isolate and handlewhen direct current sides are grid-connected is also avoided.