Electrochemical deposition is a new technique for preparation of calcium phosphate coatings on metallic orthopaedic implants. However, existing studies on this technique are primarily empirical and systemic studies are lacking. The present study attempted to address these limitations by rational establishment of coating conditions and investigation of mechanisms. Methods First, a calcium phosphate precipitation boundary curve was established by titration under a constant Ca/P molar ratio, and then four working solutions were selected based on this curve. Subsequently, cathodic reactions in the four solutions were determined by linear sweep voltammetry, and optimal potential range was selected based on the voltammograms. Results The precipitation boundary curve of calcium phosphate solution was obtained by titration and found that when the solution pH was below the boundary of 0.7-1.2, the solution remained stable for more than 3 days and the coating could be formed. The range of the electrochemical deposition potential is approximately-1.0 to -1.2 V. When the pH was controlled ~1.0 below the precipitation boundary, -1.15 V was selected as the working potential, uniform coatings consisting predominantly of octacalcium phosphate were prepared on titanium from all four working solutions. Current-time curves were fitted to the Cottrel equation, indicating a two-phase pattern: initial driving force provided by reduction of H+, and sustained calcium phosphate crystals formation driven by reduction-splitting of water molecules.Conclusion The key factors affecting electrochemical deposition of calcium phosphate coatings are successfully determined and the coating formation mechanism is elaborated. Moreover, coating conditions are similarly established for tantalum, indicating this mechanism-based approach to be a robust and for designing coating techniques for various metallic implants