The invention provides a fault crossing control method and system for an offshore doubly-fed wind turbine. The method comprises the steps that when a fault occurs, whether the terminal voltage exceedsthe limit is determined according to the collected terminal voltage of the offshore doubly-fed wind turbine; if the terminal voltage exceeds the limit, an offshore wind power grid-connected system enters a low-voltage duration, and preset active and reactive power coordinated control is performed; and if the terminal voltage does not exceed the limit, and if the time at which the terminal voltagereturns to normal is within a time threshold, the offshore wind power grid-connected system enters a post-fault clearance stage and executes reactive support exit control. The method and system takeinto account the transient characteristics changes caused by high-voltage alternating current transmission cables of offshore wind power, perform active and reactive power coordinated control during low voltage periods, and perform reactive support exit control after fault clearing. The fault ride-through capability of the offshore wind power grid-connected system is improved. The stability of theoffshore wind power grid-connected system is enhanced.