Plant species diversity is one of the critical factors for maintaining multi-function and stability of terrestrial ecosystem. We reviewed the traditional methods for measuring plant species diversity of grassland (PSDG), and then introduced the new ideas and methods used for PSDG monitoring. Traditionally, PSDG monitoring depended heavily on ground-based investigation, which usually required large amounts of time, labor, and cost, and therefore was only suitable for small scale investigation. Grassland plant species were typically small in size and highly mixed. It was difficult to identify and measure by remote sensing due to the limitation of resolution. Consequently, most studies on PSDG were based on remote-sensing retrieval or habitat simulation. Characterized with high spatial-temporal resolution, flexible and low cost, the unmanned aerial vehicle (UAV) technology was regarded as the bridge between ground-based investigation and satellite remote sensing. It could be the breakthrough for monitoring PSDG