Iridium layer was prepared on platinum substrate under constant current in aqueous system using anhydrous iridium chloride as precursors. The surface morphology and the composition of the iridium layer were characterized by SEM, EDS and XPS. The optimized condition was derived. The results show that the concentration of iridium chloride has great influence on the surface morphology of the iridium layer. When the concentration is low, too thin iridium layer is formed, resulting in peeling or cracking. Therefore, an appropriate increase in the concentration of the precursors will help to improve the quality of the Ir layer. In a certain range of pH values, the surface morphologies of the iridium layers prepared on different conditions are nearly the same. The surface is smooth and iridium particles are uniform and dense. Current density has great influence on the surface morphology of the iridium layer, especially on the size and the density of crystalline particle. The iridium layer cannot be deposited at low solution temperature. Whereas the iridium layer is rough and its surface morphology is uneven at too high temperature.