The work aims to solve the problem in the efficient preparation of electro back-scattered diffraction sample, lay foundation for high precision electron microscope analysis and obtain the appropriate electro-polishing parameters. The raw steel material was electro-polished after being mechanically polished by standard metallographic techniques. The DC constant power supply was used in the electro-polishing test and the mixture of phosphoric acid and sulfuric acid acting was adopted as the electrolyte. The electro-polishing test was conducted under different combination of parameters, including voltage, current and temperature. Then the polished surfaces of samples after the test were examined and shot by optical microscopy and scanning electron microscope. In the test to determine the optimal voltage, electro-polished surface was corroded at the voltage of 5~10 V. More striations were found at the voltage of 10~15 V. A little striations were found at the voltage of 15~20 V. In the test to determine the optimal current, electro-polished surface was corroded at the current of 2~3 A. A little striations were found at the current of 3~4 A. Over corroded surface was found at the current of 4~5 A. In the test to determine the optimal temperature, a little striations were found at the temperature of 40~50 ℃. Little striations were found at the temperature of 50~60 ℃. No striations were found at the temperature of 60~70 ℃. The polishing quality of electro-polished surfaces highly depends on the electro-polishing parameters. Compared to the voltage and temperature, the current is the parameter with the most influence on the electro-polished surface. From the analysis, the optimal parameter conditions are the following: the voltage of 15~20 V, the current of 3~4 A and the temperature of 60~70 ℃.