Abstract: This paper tells about how to calculate the inverted population density by using the rate equation of quasi three-level system when the Laser resonant cavity is in a steady state,and to set up the steady-state equation which satisfies the in-tracavity foundamental mode’s oscillating.From the close valve value,the pumping rate (Rth),and the corresponding valve value rate (Pth) can be obtained.At last,the frequency multiplier efficiency can be calculated through analysing the theory of intracavity frequency multiplier.

Key words: rate equation of quasi three-level system, valve value rate, frequency multiplier efficiency