The work aims to improve surface quality of copper, control copper removal in scope of application, and study electrochemical polishing solution ratio and optimum process parameters. The electrochemical polishing was applied to workpiece in a self-assembled electrochemical polishing system. Surface roughness and mass of the workpiece before and after processing were measured and recorded with a 3D surface profiler and precision electronic balance, respectively. Experimental scheme was designed in the combined method of single factor experiment and orthogonal experiment. The effects of phosphoric acid concentration, electrolyte temperature, voltage, duty cycle, frequency and processing time on surface roughness of copper, and the effects of additives on experimental results were studied. Influence curve of phosphoric acid concentration and temperature on surface roughness was obtained. Influence trend of voltage, duty cycle, frequency and processing time on surface roughness, and also optimal parameters were obtained by means of range analysis. After ascorbic acid was added into the solution, material removal rate was reduced to below 1000 nm/min while surface roughness was up to 75 nm. After ascorbic acid and ethylene thiourea were added simultaneously, material removal rate was 400 nm/min and surface roughness was as low as 17 nm. Optimal parameters of electrochemical polishing were: voltage 10 V, duty ratio 23%, frequency 23 kHz, processing time 11~14 min, and solution ratio was as follows: 55% phosphoric acid, 0.3% ascorbic acid and 0.2% ethylene thiourea. The material removal rate can be effectively controlled by adding ascorbic acid, and the surface roughness of copper can be reduced by adding ascorbic acid and ethylene thiourea simultaneously.