Abstract: There are many effective computer programs for applying IRT models in the world, such as BILOG, RUMM, MULTILOG, PARSCALE. But these programs are not easy to be manipulated, especially for those who are not very familiar with IRT. These programs run in DOS mode, where commands are typed into a text file and then submitted. For the purpose of being more widely used with IRT, we discussed the realization of parameter estimation techniques for IRT multiple category scoring model, and developed a computer program called GES. GES is developed with object-oriented mode, and so it is very easy to be operated. To calibrate the program, analysis of five Monte Carlo simulated data sets were used in this study. And the results showed that GES is valid, also we found that the stable and validity of parameter estimation would be violated if the amounts of sample are too small

Key words: Item response theory, multiple category scoring model, parameter estimation, GES