During the construction of diaphragm wall using hydraulic grab， the grab needs to maintain vertical to ensure the accuracy of the side wall trench formation. When the excavation part of the grab interacts with the soil， the load acting on the grab has the characteristics of transient multidirectivity and non-uniformity， which leads to the deviation of the grab lowered by the steel rope and damages of the verticality of the trench wall surface. This article established a multi-body dynamic model of hydraulic grab and a clay soil layer model. Through the combination of multi-body dynamic and discrete element method， the tilt of the grab during the construction process of the hydraulic grab in the clay soil layer is analyzed， and an electro-hydraulic proportional speed control circuit to control the movement of the main hydraulic cylinder of the hydraulic grab is designed. Through joint simulation， the influence of the control signal of the main hydraulic cylinder on the tilt process of the grab is emphatically discussed， which provides a basis for further research on the hydraulic grab deviation correction system and control strategy.