Using four extremely early-maturing and three early or medium-maturing varieties, crop photosyntesis and respiration in the field were measured 20-30 days intervals from 50-20 days before to 20-40 days after heading. The temperature coefficient of respiration(Q_<10>) was linearly increased from 1.21 to 2.52 according to the growth stage. Crop respiration under the growing temperature was changed curvilinearly and showed its maximum value at about 10 days before to 10 days after the heading time, which was slightly later than gross photosynthesis under thelightintensity of10or06ca1/cm2 The ratio of respiration to photosynthesis (R/P ratio) was increased associated with the growth stage, and in the ripening stage, the R/P ratio of extremely early-maturing varieties which were matured under high temperature, was about 10 to 30% higher than that of early or medium maturing varieties.