The invention provides a reaction system for cultivating microalgae and preparing bioenergy, which comprises a microalgae cultivation system and a bioenergy preparation system, in particular to an algae suspension collecting tank (1), an algae suspension delivery pump (2), a photoreactor (4), a gas storage tank (6), a plate frame filter (9), a filtrate storage tank (10), an extraction tank (12), an extraction separating tank (13), an extraction distilling still (14), a grease cooler (15), an ester exchange reaction kettle (16), an ester exchange cooler (17), an ester exchange separating tank (18), an ester exchange distilling still (19), a finished product cooler (20), a fermentation tank (21), a gas collecting tank (22), a solvent oil storage tank (25), a methanol storage tank (26) and the like. The reaction system integrates an algae photoreactor, a collecting device, an oil extraction device, an esterification device and a fermentation device into a whole, realizes the continuousness of raw material oil production and bioenergy preparation and has compact structure, high utilization rate and low cost.