Abstract: Localization is significant for various applications in Wireless Sensor Networks. It is found that the estimated hop-distance will affect localization result. In this study, we propose a Cosine Theorem-based DV-hop localization algorithm (CTDV-hop) to improve localization precision. After estimating the average hop-distance by the traditional DV-hop technique, we select the middle node between every two anchor-pairs in the transmission route one by one. Then the estimated hop-distance is adjusted by the angle between the anchor-pairs to that selected middle node. We hence obtain the improved localization results and can accurately locate even the distribution of nodes is non-uniform. The simulation results illustrate that the CTDV-hop algorithm effectively improves the localization precision without extra energy consumption in networks.