The invention discloses a meteorological window forecast system and a meteorological window forecast method for the marine floating and immersion of immersed tube tunnel tube sections. The system comprises a monitoring mechanism, a processing center and a client terminal, the monitoring mechanism, which is arranged at a construction site, comprises a water flow monitoring device, a wave monitoring device, a wind monitoring device, a tube section external force monitoring device, a tube section internal force monitoring device and a tube section posture monitoring device, the processing center comprises a tube section stress and stability analysis device and a construction operation time window forecast device, the data transmitted to the processing center are processed by the tube section stress and stability analysis device, so that stress and stability calculation results for tube sections are obtained, and the construction operation time window forecast device screens the stress and stability calculation results and transmits meteorological and hydrological limitations and a construction operation time window to the client terminal. The marine tube section construction operation time window forecast system and the marine tube section construction operation time window forecast method for real-time monitoring, analysis and forecasting can provide accurate construction environment forecasts and constructible time windows for on-site tube section construction.