An optical apparatus based on substrate curvature method was developed for stress measurement of thin films, which offeres such advantages as overall field, non-contact, high precision, nondestructive, easy operation and quick response. Using the apparatus, the residual stress in porous silicon (PS) layers prepared by electrochemical etching using a solution of HF/ethanol with composition ratio of 1∶1 on heavily or gently doped (100) silicon as a function of the electric current density were obtained. It is found that the residual tensile stress tends to increase with the porosity increasing and the doping concentration of the silicon wafer increasing. The results show that there is a deep connection between the micro-structure PS and the residual stress distribution.