The calculating formula for suspended length during resonance are derived made out through the analysis of the underwater suspended vibration pipeline and by the utilization of resonance conditions.

Comparing rigorous numerical result with approximate formulae, we find that the reflectance formula of general thin optics can easy straight calculate the side bands reflectance of resonance filter.

Then the formula of the multiphoton resonance ionization in a linear polarization laser field was obtained and it is compared with the experiment.