A instant air dissolution flotation method was used to harvest microalgal cells from culture to evaluate its feasibility. Effects of microalgae cell density, coagulant dosage, flocculant dosage, surfactant dosage and duration of air dissolution on recovery rate were studied by orthogonal experiment. The results show that the optimal recovery rate reaches 89.57% under one of the test combination conditions. The factors can be ordered by coagulant dosage, cell density, flocculant dosage, air dissolution duration and surfactant dosage according to their effect degree on recovery rate, and coagulant dosage, cell density were the marked factors when confidence level was given as 90%. Under test conditions, recovery rate rides up when the coagulant dosage increase, and the optimal dose of flocculant appears at 20 mg·L-1. As seawater medium contains salts which own the similar fuction like surfactant, surfactant do not affect the recovery rate significantly. The time of air dissolution should not be too long, a 2-second duration is enough to providing dissolved air, and the recovery rate may reduce because of the disturbance induced by the redundant air.