Mixotrophic microalgae have demonstrated great potential for wastewater nutrient removal. How autotrophy/heterotrophy shares affect nutrient removal as well as carbon budget has not been understood. In this study, the autotrophy/heterotrophy shares in mixotrophy were quantified, and N removal rate and carbon budget under different mixotrophic autotrophy/heterotrophy shares were modeled. The results showed that mixotrophic N removal rate reached 2.09 mg L(-1)h(-1), which was 53.18% and 37.98% higher than removal rates in autotrophic (0.97 mg L(-1)h(-1)) and heterotrophic (1.25 mg L(-1)h(-1)) controls. Mixotrophic-autotrophy and mixotrophicheterotrophy contributed 1.15 mg L(-1)h(-1) and 0.94 mg L(-1)h(-1) in N removal, respectively. Model disclosed that at balanced share of 6:4, more than 2 mg L(-1)h(-1)N removal could be achieved, similar to bacterial nitrogen removal rate but with a negative carbon budget of 6.21 mg L(-1)h(-1). Nutrient removal using mixotrophic microalgae would lead to carbon negative sustainable wastewater treatment and resource recycling.