Abstract: Objectives: Since the high frequency of extreme weather, the railway subgrade disaster shows a trend of increasing, great harmfulness and hard to detect in advance. Even a small-size subgrade disaster may cause the train services to be paralyzed, which prevents the development of transportation. Many incidents illustrate that the earliest subgrade disaster always appeared in areas where no case ever reported before. It meant that traditional monitoring methods are hard to detect the hidden danger area. Thus, a promising method is urgent need to be proposed for meeting the monitoring requirement for train safety operation. Methods: Therefore, the characteristics of subgrade disaster was summarized under different disaster-pregnant environments, and the advantages of various monitoring methods are discussed to find a collaborative applications method for early identifying the subgrade disaster. Results: The potential hazards that may cause damage to the subgrade structure and the deterioration degree of subgrade were considered as the main monitoring object of subgrade service status, including subgrade deformation monitoring, structural health monitoring, geological hazard monitoring along the railway, track irregularity, and external environmental monitoring. Then, an investigative approach based on the integration of space-air-train-ground muti-source techniques was proposed to detect the geohazards and monitor the service status of railway subgrade. It means that collaborative application of different monitoring methods, cooperative analysis of different scales and resolutions data and collaboration of between various railway departments were required. Two monitoring schemes for subgrade disasters and the service status of subgrade were proposed based on the integration of multi-source and multi-scale monitoring technique. Conclusions: This monitoring system had been applied in the identification of subgrade service status in the Shanghai-Nanjing high speed railway, which can quickly investigate the location of the disasters and deterioration degree of subgrade. Finally, the development direction of subgrade service status monitoring was discussed.