A LDA pumped highly stable Nd∶YLF ring laser is developed. With an output laser intensity induced negative feedback control of resonator gain, a quasi-continuous prelase with duration of ～100 μs is established, then Q-switch during this prelase. Because the prelase mode is well matched to the resonator eigenmode and with certain intensity, the build up time and intensity of Q-switched pulse are very stable. Experimental results show that intensity instability of output Q-switched pulse doesn′t exceed 4.3%, and time jitter does not exceed ±4 ns.