Polishing diamond with hot metal method was hard to get experimental data, which was very important to the process of polishing. The relationship between polishing parameters and polishing quantity cannot be easily deduced with the limited experimental data. This paper uses Rough Set method to process the data and some useful conclusions have been drawn. The load factor in polishing process can be ignored in the polishing process. In the case of engineering application, the load merely ensures the contact between diamond and hot iron metal. Other parameters, such as temperature, polishing speed and time, are important factors to the polishing quality.