The modified cross entropy algorithm and the program flow were proposed based on the combination of fuzzy C mean clustering algorithm and traditional cross entropy algorithm. This algorithm was successfully used in unequallyspaced arrays synthesis, whose number of array element are respectively 6, 8, 10, and 12, and solved the multiobjective optimization problems of the peak sidelobe level and beam width in the field of unequallyspaced array synthesis. In the corresponding cases, the balance curves to peak sidelobe level and beam width of unequallyspaced arrays were proposed.Optimization shows that, given the beam width and the number of unequallyspaced array elements,  the peak sidelobe level of unequallyspaced array was decreased by nearly 30% compared with equallyspaced array. In the uniform array beyond the cutoff distance, the algorithm more efficiently and accurately found tradeoff to peak sidelobe and beamwidth.