The two-step model of measuring corporate bond transaction cost in the inter-bank bond market is built in this paper. Using tick by tick data of inter-bank bond market, we estimate 108 corporate bonds transaction costs separately and investigate the average transaction cost of the whole corporate bond market. The results indicate that transaction cost decrease significantly with trade size becoming larger. Transaction activity, maturity and rating are determinants of transaction cost. The more active bonds, bonds close to maturity and highly rated bonds have lower transaction cost than other bonds. Such characteristics result from the special trading mechanism of inter-bank bond market. In order to lower transaction cost, the regulator should increase the inter-bank bond market transparency.