There was little information about the overcompensatory growth of microalgae due to their small body size and methodological limitation. Although some studies have shown that several microalgae such as Prorocentrum minimum, Chlorella pyrenoidosa, Tetraselmis tetrethele, and Nannochloropsis oculata had the apparent effect of overcompensatory growth after darkness stress or nutrient deficiency stress, it is unclear that whether phenomenon of overcompensatory growth is general. In order to determine the existence of overcompensation growth of microalgae, this paper examined the effects of UV-B stress on production of bioactive substances during the overcompensation of Pavlova viridis. This study included five different radiation levels, namely 4, 6, 8, 10μW•cm－2, and 12μW•cm^－2. The experimental procedure included the following two steps: First, P. viridis was treated with five different UV-B radiation levels for 10 and 15min, respectively, using normal culture condition (no UV-B radiation) as the control. Second, the UV-B stress was removed and then the treated groups and the control were simultaneously cultured for 12 days under the same inoculative density and normal culture conditions. Several parameters including OD value, contents of chlorophyll a, carotenoid, incellular protein and carbohydrate were measured. The results showed that growth of P. viridis was significantly inhibited by UV-B stress, with significant decreases (p<0.05) of 17.7%～51.5% in relative growth of group a and of 26.2%～60.0% in relative growth of group b, respectively. After UV-B stresses, however, although differences in relative growth between the treated groups and the control were not significant during the prophase (1～4d), such differences between the treated groups and the control were significant (p<0.05) or extremely significant (p<0.01) during the metaphase and anaphase (6～12d). This result suggests that P. viridis had the strong ability of overcompensatory growth under the condition of UV-B stress. The main characteristics of this overcompensation were that the treated groups had higher average relative growth rates, higher OD values and higher concentrations of chlorophyll a, carotenoid, cellular protein and carbohydrate compared with those of the control during the metaphase and anaphase (6～12d), with the highest increase of 26.6%, 29.2%, 29.9%, 15.3% and 34.4% in OD, chlorophyll a, carotenoid, incellular protein and carbohydrate, respectively. Our results also showed that the lag time for the overcompensation increased with increases in radiation intensity and duration (3～5d). This study provided strong theoretical and technological support for producing bioactive substances of microalgae resulting from overcompensatory growth after UV-B stress.