Abstract: Taking half year old Sterculia nobilis Smith seedlings as the research object, the effects of shading, fertilization and their interaction on physiological characteristics and nitrogen accumulation of Sterculia nobilis Smith seedlings were studied by two factor pot experiment with four light levels （100.0%, 41.3%, 14.3%, 3.6% natural light） and four fertilization levels （0, 2 000, 4 000, 6 000 mg/plant）. The results showed that the effects of indicators reached extremely significant levels in June, September and December, the activities of SOD, CAT and POD and N concentration in leaves were the highest in September and the lowest in March. With the gradual decrease of light intensity, the content of MDA, the activity of SOD and POD showed the trend of decreasing first and then increasing. Under the same light level, with the increase of nitrogen, the content of MDA reached the maximum at N0 nitrogen level, and the three enzyme activities under L1 light treatment were lower than those under other light conditions. Under the same nitrogen level, the content of MDA reached the maximum under L0 light condition, and the three enzyme activities were lower under N3 nitrogen level compared with other nitrogen levels. There was significant interaction between different light and nitrogen levels, according to the comprehensive evaluation of the membership function of each index of Sterculia nobilis Smith seedlings, it is concluded that the largest subordinate value of Sterculia nobilis Smith seedlings is L1N3 treatment. The research indicated that strong light, insufficient light and lack of nitrogen fertilizer were not conducive to the growth of Sterculia nobilis Smith seedlings, and oderate shading （41.3% natural light） and increasing nitrogen application （6 000 mg/plant） could effectively promote the growth and development of Sterculia nobilis Smith seedlings.

Key words: Sterculia nobilis Smith, light, nitrogen： physiological characteristics