Aiming at the durability problem of electromagnets for proportional valves of construction machinery, in order to improve the resistance of electromagnets to thermal failure under random load conditions, a parametric redesign model of proportional electromagnets was proposed based on multi-physical field coupling theory and robust optimization theory. By taking a proportional electromagnet with basin-type suction structure as the research object, the effectiveness of the proposed parametric model was verified through steady-state electromagnetic test and temperature distribution test. Under the premise of ensuring the accuracy of electromagnetic calculation, the parameters such as magnetic conductivity and heat transfer with fuzzy magnitude in the system were calibrated. With the main structural parameters of electromagnet and coil as control factors, and with the random error of wire diameter of coil enameled co-pper wire caused by the uncertainty of production process as noise factor, orthogonal tests were designed based on Taguchi method, and the evaluation function of the thermal robustness redesign of multi-factor weighted proportional electromagnet was defined. Then, with the thermal load of the proportional electromagnet obtained in the field test of the excavator as the response calculation heat source, the redesign of the key structural parameters with the minimum system response variation under noise disturbance was carried out, under the constraint of allowable temperature rise that does not cause the coil insulation failure. The results show that the coil length and the number of turns are the main factors affecting the thermal robustness of the electromagnet, and that the coil window shape determined by the winding process determines the magnetic permeability and heat transfer capability of the system. The thermal robustness redesign method of proportional electromagnet proposed in this paper is of engineering reference value for the custo-mized design of electromechanical products under magneto-thermal coupling.