This paper analyzes, with single energy-level recombination-centre model, the phase-shift lifetime of excess carriers in semiconductors under sinusoidal injection. Hence are obtained the difference and sameness between phase-shift lifetime and static state lifetime as well as transient state lifetime:1. The phase-shift lifetime in relation with the injection frequency decreases as the frequency increases.2. Under low frequency injection, the phase-shift lifetimes of electrons and holes are the same and equal to transient state lifetime.The conditions of low frequency injection are discussed in this paper.