Topology control is an effective method to improve energy-efficiency and increase the capacity in Wireless Sensor Networks (WSNs). To fully characterize WSNs with lossy links, we propose a novel probabilistic network model. Under this model, we meter the network quality using network reachability defined as the minimal of the upper limit of the end-to-end delivery ratio between any pair of nodes in the network.We attempt to find a minimal transmitting power for each node while the network reachability is above a given application- specified threshold, called probabilistic topology control (PTC). We prove that PTC is NP-hard and propose a fully distributed algorithm called BRASP. We prove that BRASP has the guaranteed performance. Two rules that must be followed by any algorithm have been identified. We conduct both simulations and prototype implementations based an 18-TelosB-node test- bed. The experimental results show that the network energy- efficiency can be improved by up to 250%. The average node degree is reduced by 50% which will lead to a great benefit for the network capacity.