Piled rafts have been proved to be an effective and economical foundation to control total and differential settlements as well asimprove bearing capacity. Piled raft foundations are loading systems that load transfer is transmitted by them and are pile groups that cap in them has the bearing effect. Particularly in the soft clay these systems are used in heavy structure, bridges foundation and heavy machinery foundations. In general pile groups are added to the following two reason: First, bearing capacity of raft foundation for endure of exerted load is lower than sufficient quantity. Secondly, bearing capacity of raft foundation is sufficient, but differential and general settlement of foundation is greater than allowed value.The conventional design of a piled foundation is based on a bearing capacity approach, and neglects the contribution of the raft. Pile groups are frequently designed with equal or similar pile lengths. However, the signi?cant interaction effects among equal-length piles imply that this may not be the optimized con?guration. This paper presents the optimization analyses of piled rafts and freestanding pile groups, where pile lengths are varied across the group to optimize the overal foundation performance. In a piled raft, the length and arrangement of piles has a signi?cant effect on the stresses and de?ections of the raft. The use of piles with different dimensions and properties below a raft is an innovative concept and can optimize the design of a piled raft.The behavior of a piled raft is affected by the 3D interaction between the soil, piles and raft. Numerical methods, which are approximate, have been developed widely in the last two decades because numerical methods are less costly and may be used to consider many kinds of different soil and foundation geometries compared to ?eld and model tests. In this study Piled raft foundation is based on settlement control, changes the dimensions and system arrangement is done for reducing of settlements and lateral deflection of system. In this study, finite element approach has been used. Piled raft foundation is linear elastic and soil are assumed to have Mohr-Coulomb model and elastoplastic. Studies on parameters like distance between piles, length of piles, diameter of them, different vertical and lateral loading magnitude, number of piles and piles to soil modulus of elasticity proportion for two models of pile group with same length and different length (constant sum of pile length) is done. Increasing of vertical bearing areas, piles distance, diameter of piles, ratio of modulus of pile to soil and increasing the over length of the piles to reach the over length of vertical bearing are effective parameters to reduce the lateral changes. For the pile group raising of the length of the internal piles and decreasing of the length of the external piles has positive influence on vertical settlements of the system, but if length of the identical piles is less than overlength of vertical bearing, with decrement of the length of the internal piles and increasing of the length of the external piles, lateral deformation of the center of the raft foundation is reduced. Otherwise, changes in piles length haven’t any effect on the system deformation, chiefly in low safety factors (about 2 to 3). Keywords: Piled raft foundation, finite element method, parametric analysis, mohr-coulomb model.