In this paper, we address the problem of sound source localization in reverberant environments. Time-delay estimation (TDE) methods are widely employed to locate sound sources based on the time differences of arrival (TDOAs) of signals received at different microphone pairs. In strong reverberations, the highest peak of the localization function is not necessarily from the true source resulting from the multi-path effect. Our previously proposed method based on the optimal peak association (OPA) aims to extract multiple peaks from the localization function for each microphone pair and find out the optimal association of TDOAs corresponding to the same sound source. However, due to the limitation of geometric configuration of microphones and possible missed detections, some microphone pairs fail to provide high-quality TDOA measurements. An improved OPA method is developed in this work based on the robust least squares which can determine the weights adaptively in terms of their respective observation accuracy. Experimental results demonstrate the superiority of the proposed method compared with the original OPA method in reverberant environments.