The default risk comes up gradually in the meanwhile China’s government push on Supply Side Structural Reform and deal with debt dissolving problem. Apparently，the credit market sees the divergence trends. Trust financial companies cannot emphasize the selective client strategy，selective risk management，and fending off major risks any more，during the period of chopping the nonstandard debt financing business. Therefore，they must establish the strict risk controlling system and develop the powerful tools. This paper discussed the importance and necessity of the internal credit rating system. The readers can clearly see the the methodology and procedure of developing the credit rating system by the example of real estate firms.