► Carbohydrates from microalgae can be a promising feedstock for yeast culture to produce biofuels. ► Pretreatment of microalgae and carbohydrates extraction from algal cell were performed. ► Four factors of ultrasound assisted extraction were examined by fractional factorial design. ► Refined model was confirmed as a good fitting model via analysis of variance (ANOVA). ► Yeast biomass of the group with glucose from microalgae was much higher than that of control group. Recently, carbohydrates biomass from microalgae is considered as a promising and inexpensive feedstock for biofeuls production by microorganism fermentation. The main obstacle of the process is microalgae pretreatment and carbohydrates extraction from algal cell. In this study, comparison of three pretreatment methods was performed and the results showed that ultrasonic assisted extraction (UAE) was very effective. The effects of four parameters (ultrasonic power, extraction time, flow rate and algal cell concentration, respectively) on extraction efficiency were also investigated. Additionally, in order to identify significant factors for glucose yield, combination of these four parameters was examined by using fractional factorial design (FFD) and the regression model was obtained. Meanwhile, the refined model was confirmed as a good fitting model via analysis of variance (ANOVA). After extraction, glucose obtained from microalgae was used as substrate for Rhodosporidium toruloides fermentation and yeast biomass was much higher than that of control culture.