Frequency pulling effect is a very important content in laser theory. In classical laser theory, it is usually derived and discussed using laser resonant condition and gain medium dispersion, which is somewhat difficult to understand. In semiclassical laser theory, an expression similar to the “center of mass equation” can be obtained by expanding the gain medium dispersion with laser frequency to the first order. Based on this expression, this paper establishes and discusses the physical picture of frequency pulling effect, and extends it to a more general “laser” theory. With two important teaching cases of ring laser gyroscope and active optical clock, we can help students understand the physical picture and capturing the physical origin of the frequency pulling effect. It has certain reference value for improving the teaching effect of frequency pulling effect.