With the aim of isolating a high biomass accumulation strain and optimize environmental factors to enhance its biomass production, an unicellular green algae was isolated from fresh water samples, the morphological and genomic characterization identification of this strain was carried out by using 18s rRNA and ITS1 analysis. This newly isolated strain named EJ12-3 was identified as Desmodesmus sp. The environmental factors for biomass production of Desmodesmus sp. EJ12-3 was optimized by using response surface methodology (RSM). The experimental and the predicted values were very close which reflected the accuracy and the applicability of RSM (R2＝0.950). According to the results, the optimal condition for biomass production within the experimental range of the variables studied was: temperature of 28℃, light intensity of 131 μmol/(m2·s), light/dark cycle of 15∶9 and pH value of 6.0. Under this condition, the predicted biomass production value was up to (0.648±0.015) g/L.