The work was aimed to the study the 137Cs and 131I transport dynamics along the trophic chain, from the atmosphere to soil, vegetation, dairy cattle, milk, and the human body. This was done with the use of the radioecological simulation model based on instrumental data from the “Warsaw” scenario of the International Atomic Energy Agency’s (IAEA) EMRAS project, which were collected after the Chernobyl nuclear accident. The created simulated radioecological model was used for reconstruction of the 131I radioactivity in dairy cattle milk in the Warsaw and Ostroleka areas located in the central part of Mazovia, where the cattle dairy milk radiometry was performed in April-May 1986. The aim of the study was to verify the radioecological model, to assess the reliability and uncertainty of the milk block of the computed model. It was found that the successive account of discrepancies between computed and reconstructed instrumental data of 131I radioactivity dynamics in green fodder on farms in Mazovia areas and the shortage of clean fodder stocks harvest lead to a successive improvement of the agreement between computed and instrumental data of 131I activity in the dairy milk. For all variants of accounting correction the ratio of computed data to instrumental data with recalculated 131I activities in the atmosphere of the Ostroleka Area is on average 2.5–3 times closer to their ideal value of 1 than in calculations with instrumental data for a cloud. The prognostic properties of the computational model at the stage of reconstruction of the specific 131I activity in milk, estimated as the ratio of computed data to instrumental data, can be estimated as 1.05±2.0; the values of these ratios for correction of thyroid radiation doses to the population due to the contaminated milk consumption are estimated as 1.3±2.5.