Abstract: In order to make use of interspecific competition to co-culture beneficial microalgae and build excellent algal forms in ponds, we designed different temperature gradients (10, 15, 20, 25, 30 and 35 ℃) and different initial density ratios (Navicula pelliculosa∶Chlorella vulgaris was 1∶10, 1∶1, 1∶0.1, respectively) for an experiment, and investigated the effects of temperature and initial density ratios of N. pelliculosa and C. vulgaris on their growth and competition. The results show that the cell density of N. pelliculosa in mono-culture group increased first and then decreased at 10−15 ℃, and increased gradually at 20−30 ℃ with a maximum value of 0.50×10⁶ cells∙mL⁻¹; 25−30 ℃ was the optimal growth temperature for N. pelliculosa which could not survive at 35 ℃. C. vulgaris grew slowly or even stopped at 10−15 ℃, but grew rapidly at 20−35 ℃ in mono-culture group. The maximum value of the cell density was 14.15×10⁶ cells∙mL⁻¹. The optimal growth temperature was 35 ℃. The growth rate of N. pelliculosa in mixed culture group was higher than that in mono-culture group, and increased gradually with increase of proportion of C. vulgaris. The maximum cell density of N. pelliculosa in mixed culture group was significantly higher than that in mono-culture group. The smaller the initial cell density was, the faster C. vulgaris grew in mixed culture group. The growth rate of 1∶0.1 group was significantly higher than that in mono-culture group, and the growth rate of 1∶10 group was significantly lower than that in mono-culture group. The competitive inhibition parameter shows that C. vulgaris had little competitive inhibition on N. pelliculosa. The competitive inhibition parameter of C.vulgaris against N. pelliculosa (α value) increased with increase of temperature and proportion of C. vulgaris, while that of N. pelliculosa against C. vulgaris (β value) increased with increase of temperature and proportion of N. pelliculosa. The two microalgae can coexist peacefully.