Continuous monitoring of stored CO2 is strongly required to achieve safe and effective CCS. We first introduce our recent studies focused on developing a continuous monitoring system based on portable active seismic source(PASS)and distributed acoustic sensing(DAS). For the continuous analysis of this monitoring data, machine learning emerges as a valuable tool, enabling automated seismic interpretation. These monitoring technologies including machine learning should be optimized for each CO2 storage site. Moreover, integrating the monitoring outcomes into CO2 behavior modeling(i.e., reservoir simulation)is crucial to predict the future fate of stored CO2. The geologic model for the reservoir simulation should be updated(or improved)by reflecting the continuous monitoring data. Our modeling study particularly emphasizes the integration of molecular-scale and pore-scale CO2 behaviors into reservoir-scale simulations, aiming for an accurate description of CO2 behavior within the reservoir.