The acoustic emission phenomena generated by the laser welding process are closely related to the keyhole forced oscillation and the dynamic pressure balance at the keyhole bottom. In this study, we constructed the mechanical equation of keyhole bottom pressure balance and used the “electro-mechano-acoustical” analogy theory to convert it to the acoustic equation, the acoustic resonant frequency as well as the magnification amplification factor of the keyhole oscillation in different penetration states were derived. The monitoring platform of acoustic sensor and high-speed photography was established to obtain the acoustic emission signals and lateral keyhole images. The acoustic features and image features extracted from the monitoring data provided a strong validation for the derived formulas, and the acoustic phenomena of different frequency-energy components were explained according to the derived formulas in turn. The results showed that the derived theory is compatible with the experimental comparisons, demonstrating the great interpretability and applicability. The introduced analogy theory can establish a bridge between keyhole forced pressure and acoustic emission vibration, which can help to reveal the characteristics of keyhole oscillation mechanism. A novel model of keyhole oscillation was proposed and verified using process monitoring data in this study, which provides a new approach for the investigation of keyhole dynamic.