There is substantiated in the article suitability of carrying out experiments on research of waste decomposition processes on model samples in bioreactors. To assess in situ condition and impact of municipal solid waste (MSW) landfills on environment it is necessary carrying out long-term laborious full-scale observations. Thus more attention should be paid to calculation methods of assessment using laboratory research results obtained in bioreactors. There are simulated with high reliability conditions of going on biochemical processes in landfill body. It gives an opportunity to choose needed mathematical models and to correct their parameters. Using the specified methods allows in a short time to obtain necessary information on waste decomposition processes in landfills, to assess biogas potential, degree of their mineralization at various stages of biochemical processes and to choose measures for aftercare phase.