In order to evaluate bed load sediment transport in an irregular wave current coexistent field, a series of experiments were completed in laboratory with an irregularly oscillating tray, which was specially designed to simulate the irregular wave current coexistent field. Experimental results are presented on the initial motion of sediment and the rates of transport over flat horizontal bed. Testing conditions included three interaction angles, 0°, 45°, 90° and six kinds of grain sizes. Four kinds (0.2mm, 0.46mm, 0.85mm and 1.3mm) were used for the tests of initial motion, while the other two kinds (0.38mm and 1.1mm) for the tests of transport rate. Comparisons between experimental results of initial motion and modified Shields curve indicate that the Shields curve is still valid for the case of irregular wave current coexistent field. Analysis of flow regime shows that initial conditions fall within smooth turbulent transitional region. The results of transport rate show us that net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress and mean shear stress. A dimensionless formula is proposed on the basis of mechanism “Waves erode sediments, tides transport sediments”. [WT5”HZ] In order to evaluate bed load sediment transport in an irregular wave current coexistent field, a series of experiments were completed in laboratory with an irregularly oscillating tray, which was specially designed to simulate the irregular wave current coexistent field. motion of sediment and the rates of transport over flat horizontal bed. Testing conditions included three interaction angles, 0 °, 45 °, 90 ° and six kinds of grain sizes. Four kinds (0.2mm, 0.46mm, 0.85mm and 1.3mm) were used for the tests of initial motion, while the other two kinds (0.38 mm and 1.1 mm) for the tests of transport rate. Comparisons between experimental results of initial motion and modified Shields curve that the Shields curve is still valid for the case of irregular wave current coexistent field. Analysis of flow regime shows that initial conditions fall within smooth turbulent transitional region. The results of transport rate show us th at net sediment transport rate can be expressed as the function of the maximum bottom shear stress and mean shear stress. A dimensionless formula is proposed on the basis of mechanism “” Waves erode sediments, tides transport sediments. “[WT5” HZ]