Purpose. The research was carried out to improve the design process of the balancing unit for portal crane. In order to achieve the purpose one should: 1) to develop a dynamic and mathematical model that allows describing the movement of balancing unit and the boom system of portal crane, when derricking; 2) to propose the way for determining and the methodology for calculating the array of variable design parameters of balancing units; 3) to calculate the optimal ratio of the beam mounting coordinates for balancing units and to study their influence on the imbalance of the portal crane boom system. Methodology. To determine the kinematic characteristics of the balancing unit links, dynamic and mathematical models, describing the movement of balance beam with counterweight when derricking, have been developed. The task of balancing boom systems of portal cranes is reduced to determining the design parameters of the device, which would provide balancing of the boom system on the entire range of derricking. It was also developed a methodology for calculating the acceptable varying design parameters of balancing units, taking into account the conditions of mobility, assemblability and the requirements for the values of unbalanced boom torque. Findings. Based on mathematical calculations and computer simulation the expediency of using the proposed methodology for determining the design parameters of balancing units has been scientifically substantiated. The developed array of variable data makes it possible to take into account the nature of balancing and optimize the design of counterbalancing devices and boom systems for portal cranes. The authors analyzed the influence of variable parameters on the generally accepted criteria for assessing the quality of the articulated boom system: the system's unbalance, the weight of counterweight, the indices of load and boom unbalanced moments. Originality. For the first time, a methodology for determining an array of variable data has been proposed. It makes it possible to form the array of rational design parameters of balancing units. It was developed a local program for complex optimization synthesis, which makes it possible to determine the optimum ratios of the balance beam coordinates, under which the conditions of balance and quality of the portal crane are satisfied. Practical value. The proposed methodology for determining the array of varying design parameters can be used in the development organizations for designing new and retrofitting the existing balancing units for portal cranes with articulated boom systems. The proposed methodology was tested at the launch of complex optimization synthesis with respect to cranes, the configuration of which ensures assemblability and mobility of the links of all systems.