Based on eddy-covariance measurement data in Jan.～Jun., 2003 at 23m high, the changing characteristics of CO_2 flux in artificial mixed forests are investigated in typical subtropical red soil hilly area. Research result indicates that forest carbon sink/source is higher in forenoon (8:00～12:30)/first half night(0:00～5:30)than afternoon(13:00～18:00)/latter night~(18:00～ 23:30) and the average sink is 6 times of source. This ecosystem represents an important sink to atmosphere. Respiration has more positive ...