At the moment, the design of wireless networks mainly takes approximate methods of calculation not considering non-uniformity of the environment of distribution, since it is necessary to conduct labor-consuming measurements. The article shows a study on the reliability of data transfer between nodes on the wireless sensor network (WSN). The model of reliability of the network is represented considering its topology, evaluating telecommunication equipment and signal attenuation in the building. The article considers the reliability model capable of being in two characteristic modes: in a mode of full implementation of function, or in a mode of total failure of function. The article reveals research results on the analysis of radio propagation inside the building compared to propagation in unlimited environment outside the building. During the experiment a corrective coefficient was defined for calculation of network’s reliability. The article describes radio propagation problem in buildings taking into account the existence of walls and baffles in the building. These obstacles create a non-uniform environment for radio propagation of purity of 2.4 GHz and 5 GHz. Results of radio propagation significantly differs from radio propagation in free environment. The article provides the research and the analysis of the influence of propagation conditions of radio waves on the wireless networks with antennas’ layout at low height and different types of environmental conditions. An experimental assessment of the influence of factors of a heterogeneous environment inside the building on the additional attenuation of the signal for frequencies 2.4 GHz and 5 GHz is also given. The prepositional model of reliability assessment having universality and having great practical value is implementable in relation to issues of the design of a wireless sensor network, the analysis of network’s throughput capacity, optimization of topology, determination of the optimum mode of its operation and maintenance. The experimental results which show influences of structural materials and separate constructional elements of the building on the nature of radio propagation are provided.