The work aims to study the effect of MPS (Sodium 3-mercapto-1-propanesulfonate) and Cl? in electroplating copper microvia filling and obtain the corresponding action mechanism model. MPS and Cl? were added into prepared electrocoppering liquid to study the effects on TP value (microvia rate) and observed by metalloscope. The effects of oxidation-reduction property during reaction were studied by measuring cathodic polarization curve and design current curve. MPS and Cu+ in single MPS system formed compounds of -S?-Cu+ and -Cu+ and the inhibition effect reached the best when MPS concentration was 6 mg/L. MPS added into basic liquid caused positive shift of cathode-current density and negative shift of equilibrium potential and inhibited the disposition of Cu+. In MPS-Cl? compound system, MPS formed compounds of MPS-Cu+-Cl? and the acceleration reached the maximum when MPS concentration was 6 mg/L and Cl? was 60 mg/L. Due to Cl?, MPS added into basic liquid caused positive shift of cathode-current density and negative shift of equilibrium potential and accelerated the disposition of Cu+. MPS can inhibit the deposition when forming compounds of -S?-Cu+ and -SO? 3-Cu+ due to lack of Cl?, but can accelerate the desposition when formimg compounds of MPS-Cu+-Cl? with Cl?. The theoretical model for compounds adsorbing at microvia bottom in form of “single molecular layer” can explain the experiment process clearly.