Traditional DV-Hop localization algorithm and Amorphous algorithm for Wireless Sensor Network (WSN) can not meet practical application with lower localization accuracy due to defects of colinearity of beacons, range ambiguity and the distance error caused by path deviation. Especially, in the node heterogeneously distributed application scenario, the problem becomes more serious. So, a Reliable beacon-based and Density-aware distance Localization Algorithm for WSN (RDLA) was proposed to improve localization accuracy. Firstly, hop threshold and reliability function of approximate equilateral triangle were employed to select the beacon nodes with small error to avoid collinear problem. Secondly, node density-aware hop distance estimation method was used to solve range ambiguity problem, and distances were cumulatived along the Shortest Hop Path (SHP) from unknown node to three beacons. This distance was amended to straight-line distance. Finally, two-dimensional hyperbolic calculation method was adopted to determine locations of unknown nodes and improve node location accuracy. The extensive simulation results by Matlab R2012a show that the Average Localization Error (ALE) of RDLA is lower than that of DV-Hop algorithm and its improvement algorithms in node uniform distribution network. Remarkably, RDLA is tremendously superior to the others with the lowest ALE in node non-uniform distribution network and C shape network, in which, the ALE is almost controlled below 28%.