Abstract: To clarify the influences of endophytic fungus Piriformospora indica(P.indica) on the growth and development of tobacco,the effects of P.indica on the net photosynthetic rate of tobacco leaf,and metabolites,the contents of total nitrogen and nitrate in tobacco at different nitrogen nutrition levels were compared via co-culture plate experiments and indoor pot experiments.The results showed that P.indica could colonize in tobacco roots,it promoted the growth of tobacco and improve the net photosynthetic rate at various nitrogen levels.At the low nitrogen level(4 mmol/L),the total nitrogen and NO3-contents in leaves of tobacco colonized by P.indica and the control(CK) presented no significant difference;however,at the high(12 mmol/L) and medium(8 mmol/L) nitrogen levels,they were significantly reduced in colonized tobacco.Furthermore,the results of metabolite analysis indicated that P.indica colonization increased the content of some products produced in the route of photosynthetic metabolism(such as glucose and D-fructose) at medium nitrogen level;it promoted the accumulation of photosynthetic products and synthetic metabolism of amino acid at high nitrogen level.Therefore,P.indica colonization played a role in regulating the metabolism of carbon and nitrogen in tobacco.