The work aims to design a heavy-duty handling mechanical device that can realize 3T1R four degrees of freedom based on cross slide principle, so as to achieve the purpose of accurate positioning, firm clamping and handling of goods through multiple degrees of freedom. The structural design and strength analysis was carried out to load-bearing bolt by analytical method and finite element method. According to analysis results, the structural improvement scheme of bolt root fillet rolling was proposed. According to the stress values corresponding to different rolling fillets, the radius-stress (r-σ) curve and polynomial of rolling fillets were obtained by Hermite method, and the structural improvement scheme was determined by derivation. Based on the radius-stress (r-σ) curve of rolling fillets, the optimal rolling radius was determined as r=4 mm. Based on PLC control technology, the hydraulically driven control system of handling mechanical device was designed. The device realized a handling load of 55 kN, the strength of bolt root increased by 59.54% and the yield limit safety factor was up to 2.4. Through structural design, the device realizes the 3T1R four degrees of freedom. Through the structural improvement, the effect of multi-degree-of-freedom handling is achieved.