Experimental dependences on bias current and physical mechanisms of 1/f noise and g-r noise (generation-recombination noise) in Optoelectronic Coupled Devices (OCDs) are studied. Experimental results demonstrate that g-r noise of OCDs emerges with 1/f noise in the range of low frequencies and both of them have a similar rule, that is to say, in the beginning, magnitudes of g-r noise and 1/f noise increase and then decrease with the bias current keep increasing. From measuring noise of the front part and back part in OCDs, it is found that g-r noise source in OCDs lies in the photosensitive transistor. Based on mechanisms of carrier fluctuation, it is discussed that 1/f noise in OCDs belongs to surface 1/f noise and g-r noise is due to trapping and detrapping processes between carriers and deep-level in the emitter space-charge region of photosensitive transistor.