Abstract: The diurnal variation of photosynthesis,photosynthetic response and CO₂ response of landscaping tree species Michelia chapensis were studied under natural urban condition by making use of Li-6400 portable photosynthesis system.The results showed that the light compensation point(LCP) of M.chapensis was 50 μmol/m²·s,the light saturation point(LSP) was 1 568 μmol/m²·s,and the apparent quantum efficiency was 0.01.It was measured that the CO₂ compensation point of the species was 122.8 μmol/mol,CO₂ saturation point was 1 761 μmol/mol,and the carboxylation efficiency was 0.03.It was demonstrated by the measurement that the diurnal variation of net photosynthetic rate(Pn) was an one-peak curve and there was no midday depression and the peak value appeared at 10:00 with 6.31 μmol/m²·s.The main physio-ecological affecting factors were photosynthetically active radiation and stomatic conductance.