Abstract: The predesigned position activation of printed circuit board (PCB) substrates is the key process for manufacturing circuits by selective electroless copper plating. A compatible Cu²⁺ solution for epoxy resin (EP) substrate was designed with copper acetate monohydrate as a catalyst precursor, thiourea as a complexing agent, bisphenol A diglycidyl ether as a prepolymer of EP, reagent 593 as a curing agent, and 1-methoxy-2-propanol as a solvent. The compatible Cu²⁺ solution was printed on EP substrate surface by an inkjet printer. Copper circuits were additively fabricated by selective electroless copper plating. Based on quantum chemistry density functional theory, the complexation reactions between thiourea molecules and copper ions were simulated in the compatible Cu²⁺ solution. The special functional groups in the compatible Cu²⁺ solution were characterized by infrared spectroscopy and Raman spectroscopy. The results show that the resistivity of copper circuits is as low as 2.62×10⁻⁶ Ω·cm attributing to the good crystallization and dense accumulation of copper grains. The adhesion between copper circuit and EP substrate is up to 5B level with the help of the modified layer. Therefore, compatible modification EP substrate to catalyze copper circuits deposition has the advantages of simple process, economic and environmental-friendly, which provides a valuable reference for compatible modification on other common resin substrates in additive manufacturing of PCB.