Six microalgaes, including Scrippsiella trochoidea, Phaeocystis globosa, Phaeodactylum tricornutum, Nannochloropsis oculata, Tetraselmis tetrethele and Haematococcus pluvialis were studied.Their fluorescent value of different kinds and concentrations of microalgaes were determined with using TD-700 Fluorometer. Compared with cell counting and chlorophyll-a content measure, it shows a very good linear interrelation between the cell density, chlorophyll-a content and fluorescent value. So the method using TD-700 Fluorometer to determine the microalgal biomass is a quick and reliable method which can reduce artificial error, increase high consistency and operational simplicity.