Abstract: Well-designed Photo-bioreactors (PBR) support high-efficiency biomass production. Methods: Flow fields of plat-plate PBR are experimental investigated with a time-resolved particle image velocimeter (TR-PIV). Results: Microalgae flow around sets of baffles improves performance of Chlorella vulgaris growth. Conclusion: The PIV-based flow visualization method benefits microalgae PBR designs, implements of high-density cultivations. The PBR structures proposed in this paper is of great supports to design and high productivity of bio-products with high added-values.