Paper considers the task of assessment of regions' economic development level using composite index assessment technology. It is proposed to design composite index by block convolution of two groups of partial indicators. First group contains indicators measured in absolute scale. Second group consists of relative measures of dynamics. For each group we proposed own procedure for data normalization and own method for data convolution in partial composite index. The procedure for identification of intervals' bounds on the composite index's scale for each level of economic development is proposed to the aim of classification of Ukraine's regions. Presented means for identification of intervals' bounds of data grouping may be used to solve other tasks independently from the way of design of composite index and set of initial indicators. The results calculated may be used in the decision-making system as source data for further calculations, as well as a criterion for determining the socio-economic development directions.