Grasslands are important ecosystems to provide various economic and ecological services. In Japan, grassland of <i>Miscanthus sinensis</i>, which is a tall, perennial grass species, has been one of the symbolic landscape and require efficient monitoring system for better management. In this study, canopy height and biomass of <i>M. sinensis</i> in semi-natural grassland are estimated using time-series UAV imagery and structure from motion (SfM) and multi-view stereo (MVS) technique. The effect of complex topography on estimation of the canopy height and biomass is analysed as well as monitoring growth of <i>M. sinensis</i>. The results showed that UAV derived maximum canopy height and biomass have significant correlation with vegetation survey data producing <i>R</i><sup>2</sup> value of 0.92 and 0.78, respectively. The effect of topographic landforms was found to be smallest on top of the hill, followed by slope. Valley-like sunken place was affected worst. Analysis using time-series UAV data revealed that growth of <i>M. sinensis</i> is different between the landforms, and the best time to estimate its biomass was different between them. In order to accurately estimate canopy height and biomass of tall grass species such as <i>M. sinensis</i>, it is important to take plant growth stage into consideration as well as topographic landforms.