The weighted sp atial smoothing (WSS) algorithm requires preliminary estimate direction of arri val o f coherent signals in the calculation of weight factors. Here a new improved weighted spat ial smoothing (IWSS) technique for the direction of arrival estimation of cohe re nt signals is proposed. It divides the array into several sub arrays with specia l s tructure, according to the different contribution to direction o f arrival estimation between the autocorrelation matrix and the cross correlation matrix . N ested spatial smoothing algorithm is applied to gain the weight matrix to decorre late and estimate the direction of arrival of coherent source signals. In c on trast to the WSS method, the higher decorrela tion performance and angel resolution are also obtained without a priori informati on and preliminary estimate angle value. Theoretical analysis and simulation r esul ts demonstrate the correctness and validity of the new algorithm.