The doubly-fed induction generator (DFIG) participating in inertia and primary frequency regulation can reduce the rate of change of frequency and steady state frequency deviation respectively. A coordinated grid frequency control strategy considering its rotor speed constraints is proposed to solve the problem that the rotor speed is easy to exceed its constraints due to the frequency deviation and differential coefficients selection when coordinating the aforementioned two frequency control strategies. Controlling the DFIG output power can ensure that the rotor speed deviation is proportional to the frequency deviation. The coefficients of frequency signal are set based on the rotor speed constraints. According to the change of grid frequency, the output power reference value is adjusted to ensure constant rotor speed and assist the frequency recovery. Simulation results verify that the proposed control strategy can effectively keep the rotor speed within its limits and enhance the system frequency stability. This work is supported by National Natural Science Foundation of China (No. 51277049).