After the fifteen years over banking, the financial tsunami reveals that Taiwan banking industry has been in a predicament. In the recent ten years, due to being impacted by the risks of the enterprise finance, the retailer finance, the overseas investment, and even the whole economic system, the banks in Taiwan not only have lost seriously, but also been managed more hardly. How to find out a profit model based on the security, the benefit, and the public welfare principles is the critical issue. The traditional loan to small and medium-sized enterprises that brings the reasonable interest gains and the overall financial intercourse spin-off benefits has become the focal point once again. In order to create the real profit, it is important to control credit risks and the cost of operation. At this time, the government implements the new Basel¢º supervisory standard with the purpose of encouraging the banks to adopt the IRB to estimate the loan credit risks. It has to meet various the lowest operational requirements and statistical analysis patterns as well as should be practiced in the banking loan business definitely. Consequently, to build an internal loan credit scoring system with the scientific method is a key point. The research aims to produce the credit scoring model using a series of logical processes, which derived from the 2,517 small business loan samples from May, 2005 to May, 2006 of one Taiwan commercial bank. It adopted WOE model to evaluate a variety of variables, and sift out the 11 representative and the statistical items. Then, following IRB standard, Logistics Regression and related statistic analysis techniques established the credit estimating method and the linked addition scoring card. Finally, the investigation employed the violation rate distribution, Lorenz¡¦s Curve, K-S Test and Log Odds to make sure the rationality and reliability. Based on this model, there are eight essential variables that affects the verification of the loan to small businesses, including customer present loan situation, the urgent of increasing the loan, repayments custom, and so on, which conform to the banking practical know-how. Therefore, the model could assist the banking employees to calculate the loan credit grades efficiently and further make the accurate judgment.