This paper presents a hybrid frequency domain method to analyze and efficiently simulate injection locked oscillators. We combine the recent general theory of injection locking with periodic transfer function (PXF) simulation of impulse sensitivity function. This hybrid method overcomes the time-consuming transient simulation and provides design insights unavailable from PXF simulation only. We apply this method to design microwave frequency divider and 8-phase inverter-based ring oscillator with multi-phase injection. The phase relation between injected signal and locked oscillator output is studied. A simulation speedup of over 1500 times is achieved. Good agreement between the proposed and traditional approach is demonstrated.