The low-altitude unmanned aerial vehicle (UAV) remote sensing uses the UAV as a support and transports various sensors to obtain high-resolution ground-based remote sensing data. The low-altitude UAV remote sensing technology has the advantages of high timeliness, high resolution, low cost, and easy control, respectively. As a useful supplement to the gap in the measurement scale between ground and high-altitude remote sensing (aerospace and aerial remote sensing), the low-altitude UAV remote sensing expands the space scale of sample squares and improves the refinement of medium and fine scale remote sensing observation information. It also realizes the rapid collection, processing and application analysis of grassland habitat information, and is an important component of the integrated monitoring of grassland "star-air-ground". The low-altitude UAV comprises the fixed-wing UAV and the multi-rotor UAV at the present time. In anyway, the low-altitude UAV remote sensing enriches data diversity, broadens the depth and scope of data, and provides benefits for monitoring and evaluation of grasslands. Aiming at ecological monitoring of grasslands, this study summarizes the application of the low-altitude UAV remote sensing at home and abroad in grassland base survey (grassland grass height monitoring, grassland vegetation cover monitoring, and grassland aboveground biomass estimation), grassland dynamic monitoring (grassland vegetation growth monitoring, grassland yield estimation and grassland and livestock balance monitoring), and grassland emergency management (grassland fire, snow disaster and biological disaster monitoring). Finally, combined with new technologies such as big data, artificial intelligence, cloud computing and Internet of Things, the shortcomings and future development directions of the low-altitude UAV remote sensing in the field of grassland ecological monitoring are analyzed, in order to provide a reference for the follow-up research on grassland ecological monitoring and smart grassland by low-altitude UAV remote sensing. There are also certain limitations to the application of the low-altitude UAV remote sensing. Firstly, the low-altitude UAV is lightweight and vulnerable to micro-meteorological conditions. Secondly, although the low-altitude UAV may be equipped with multi-source sensors, the sensors have not yet adopted the unified design standards and considered product versatility. Thirdly, the big data processing efficiency of UAV is behind schedule. Lastly, in areas of complex environmental conditions, particularly rough terrain, the operational difficulty of the UAV increased. In the next period of time, the low-altitude UAV remote sensing should fill the above gaps, and the following developments and trends should be highlighted. The low-altitude UAV remote sensing should fully integrated UAV platform and remote sensing sensor, in order to perform integration, built-in and component of UAV flight platform and load. The low-altitude UAV remote sensing should promote the integrated monitoring of "Earth-space stars" and realize the extent of the temporal and spatial scale of grassland ecological observation. The low-altitude UAV remote sensing should combine remote sensing data from multiple sources, and integrate the emerging technologies such as big data, artificial intelligence, cloud computing and the Internet of things, so as to improve the processing efficiency of UAV massive data and mine the application value of images. We believe in that as part of continuing to promote and enhance the grassland ecological monitoring network in the new era, the low-altitude UAV remote sensing with its inherent advantages would foster the development of ecological monitoring of grasslands, from traditional ground-based observation to space-based quantitative remote sensing.