Abstract: Alga-bacteria biofilms exist prevalently in natural aquatic environments and sewage biological treatment systems and play an extremely important role in removing heavy metals in water. On the basis of a series of tests, the relationship between EPS produced by Ulothrix-bacteria biofilm and cadmium removal efficiency in sewage are discussed. The results show that EPS is mainly produced by Ulothrix sp. The amount of EPS has a good correlation with cadmium removal efficiency and cadmium accumulated in biofilm. Furthermore, the EPS from Ulothrix sp. provides an improved microenvironment that has the ability to buffer the toxicity of cadmium for both symbiotic bacteria and Ulothrix sp., which maintain higher activity of the biofilm and persistent cadmium removal efficiency.