By using a modified model of lightresponse curve of plant photosynthesis, this paper studied the effects of different concentration CO
2 (380 and 600 u
mol·mol-1) on the variations of quantum yield in the vicinity of light compensation point and the Kok effect of
Koelreuteria paniculata and
Capsicum annuum L. The modified model fitted well the lightresponse curves of the photosynthesis of
K. paniculata and
C. annuum at 380 and 600 u
mol·mol-1 of CO
2, and the photosynthetic parameters estimated by the modified model were in very close agreement with the measured data. The initial slope of the curve (
φ0) was greater than the quantum yield in the light compensation point of
K. paniculata and
C. annuum, and the quantum yield in the vicinity of the light compensation point was not a constant, and did not relate with dark respiration rate. Moreover,
C. annuum at 380 and 600 u
mol·mol-1 of CO
2 did not exist Kok effect. CO
2 concentration affected the Kok effect of
K. paniculata but less affected the Kok effect of
C. annuum. It was considered that the variation of the quantum yield in the vicinity of light compensation point of
K. paniculata was come from the nonlinear response of the net photosynthesis rate to irradiance, but the Kok effect was not existed for
C. annuum.