Field experiments were conducted at Taiwan Livestock Research Institute Experimental Farm to measure the fresh and dry weights of forage production and plant height of nilegrass (Acroceras macrum Stapf) and to collect meteorological data during the growing seasons in 2002-2003. The accumulated values of daily mean air temperature (DMAT), precipitation (DP), evaporation (DE), irradiance (IR), and sunshine hours (DSH) during the growing periods of six seasons were calculated to correlate with plant height and forage production. Forage fresh weight was found linearly correlated with plant height (R2=0.786, P<0.0001) and forage dry weight (R2=0.903, P<0.0001). Changes of both forage fresh weight and plant height were shown corresponding to the accumulated values of DMAT, DP, DE, IR, and DSH. By multiple linear regression analyses, estimation of fresh-based forage production may be improved by a three-variable linear regression model (R2=0.825, P<0.0001) from DMAT, DP and IR, while plant height may be best estimated by a two-variable model (R2=0.815, P<0.0001) from DP and DE. When validating the models with another set of data from different seasons, models gave over-predicted values, particularly fresh-based forage production. Results suggest that more data need to be collected from diversified environments to establish a model for a better estimation.