Abstract <p>Travertine, a famous karst carbonate precipitate, undergoes formation influenced by the biological activities of microorganisms such as algae. Elucidating the role of biodeposition in travertine formation will contribute to a better understanding of the microstructure of travertine. This study focuses on the effects of <i>Chlorella vulgaris</i> on the deposition process of travertine under laboratory conditions. Through comprehensive analyses of physical and chemical parameters, phase structure, crystal morphology, and microbial communities in the aquatic environment, the findings demonstrated that the increase in Ca²⁺ concentration has a deleterious effect on the growth of <i>Chlorella vulgaris</i>, leading to a reduction in calcification rate. The highest rate of calcification was observed when the concentration of Ca²⁺ reached 200.98 mg/L. As the concentration of Ca²⁺ increased, the maturation of calcification crystals was enhanced, leading to a more distinct outline of these crystals. <i>Chlorella vulgaris</i> facilitates the crystallization of calcium carbonate by offering nucleation sites and templates for growth, thereby markedly enhancing the deposition process of travertine. At a moderate concentration of calcium (c(Ca²⁺) = 200.98 mg/L), an increase in the population of <i>Enterobacteriales</i> (Beneficial bacteria of travertine deposition) and a reduction in the proportion of <i>Pseudomonadales</i> (Harmful bacteria deposited by travertine) were observed, resulting in an enhanced capacity for <i>Chlorella vulgaris</i> to deposit travertine. The present study elucidates the underlying mechanisms by which <i>Chlorella vulgaris</i> facilitates travertine formation, thereby establishing a robust scientific foundation for the ecological protection of travertine landscapes.</p>