In the die casting mould design, there is some over-constrained locating which have serious influence on the manufacturing and life-span in some certain spots. In this paper, over-constrained locating of die casting mould structure was studied based on the example of slider block core pulling mechanism. Some improving measures in die casting mould structure design were presented in this paper. Changing the rigid connection between slider block and side core into floating connection, forced action can be applied on the side core by the slider block only from the necessary radial side instead of from other directions. Side core can be located according to the constraints of insert core hole. It simplified the machining and assembling of slider block core pulling mechanism. Thus, the manufacture cost of the die casting mould was also reduced.