Abstract: To explore the influence of the external environment on Pyropia haitanensis blades, the effects of different light intensity, temperature, and ratios of nitrogen to phosphorous on the growth and parthenogenesis of thallus were studied through microscopic observation and statistical analysis. When the light intensity is 10-40 μmol/(m²·s), the algae grow slowly, mature late, and parthenogenesis also occurs later; When the light intensity increased to 60-80 μmol/(m²·s), the algae growth accelerated, maturation became early, and parthenogenesis also advanced. When the temperature is 17-20 °C, the algae grow slowly, mature late, and parthenogenesis is postponed; When the temperature rises above 23 °C, the algae growth begins to be inhibited, but the high temperature promotes the maturation of the algae, and parthenogenesis also occurs in advance. The treatment group with a nitrogen to phosphorous ratio of 16∶1 grew faster than other treatment groups (1∶1, 4∶1, 32∶1 and 64∶1), the slowest rate of thallus growth was observed in the 64∶1 ratio of nitrogen to phosphorus, but it is easy to mature and prone to parthenogenesis. Therefore, at the high light intensity, high temperature and high ratio of nitrogen to phosphorus conditions, both the maturation and parthenogenesis of the algae were improved. Culture conditions have important effects on parthenogenesis of P. haitanensis.