As an important parameter in representing precipitation anomalies, water vapor flux divergence (Qv) is decomposed into three components based on the Helmholtz theorem, i.e., flow convergence caused by rotating winds (Qr), moisture advections by divergent winds (Qd) and water vapor flux divergence by large-scale airflow convergence and divergence (Qdiv). Taking the severe rainfall event caused by Typhoon Rumbia (No.18) in 2018 as an example, this paper analyzes the temporal evolutions and spatial distributions of the three components from the perspective of water vapor flux divergence and its three decomposed components. The results show that Qv only indicates water vapor accumulations, while the decomposed components can better represent their individual leading roles at different precipitating stages. The value of Qv mainly originates from Qdiv, while the positive contribution of Qr caused by the rotational wind component is better when heavy precipitation occurs. The decrease in precipitation is often caused by the inhibition effect of Qd caused by the divergent wind component. Further applications of this decomposition technique of water vapor flux divergence will potentially improve the diagnosis and prediction of typhoon rainstorms in the future.