This paper presents the numerical simulation results of cluster pumping test in a heterogeneous aquifer with transmissivity variability described by the model of a stationary random field of its logarithm with a given scale of correlation in the plan. The case of a comparable planar distance to observation wells and correlation scale is considered. The parameters of the model of transmissivity heterogeneity of the simulated aquifer have been obtained from the data of experimental tests carried out within the Yuzhno-Voronezhskoye groundwater field. The simulation has shown that the average results of interpretation of the cluster pumping data correspond to the geometric value of the transmissivity, which confirms the previously obtained approximate theoretical result for the model of small-scale heterogeneity and extends it to an important case of the similarity of cluster well test planar sizes and the spatial scale of heterogeneity. This study confirmed the possibility of applying standard methods in processing cluster pumping data under horizontal heterogeneity conditions to estimate the equivalent aquifer transmissivity in the well cluster location area.