The technical issues of EUV resist are high resolution, high sensitivity, low line edge roughness (LER), and low outgas. Between these, there is a trade-off relationship, and the most significant point in these issues is the simultaneous achievement of high sensitivity and low LER. In order to efficiently develop high-performance EUV resist, it is necessary to understand the chemical reaction of EUV resist. Thus, we have studied the EUV chemical reaction using the soft X-ray absorption spectroscopy. In this method, the absorption spectra had a lot of absorption peak which could not be assigned to the chemical bonding. For analysis of these unknown peaks, the molecular orbital (MO) calculation using the first principle, socalled "ab initio", is expected to be an effective support computation method. Since the chemicalstructural-optimization is necessary for the first-principle calculation, we introduced the MO calculation software Conflex that can search the position of reactive active molecules in the conformational space, optimize resist chemical structure, and create a resist molecular model. Based on this optimized molecular model, the MO calculation software Gaussian was performed to calculate IR spectrum. By comparing the IR spectra obtained by an experiment and the calculation, some IR peaks was assigned to a chemical group, and chemical-bond transformation was suggested. From these results, it was confirmed that MO calculation had an ability for analyze the chemical reaction of resist material. Thus, MO calculation can accelerate the development of high-performance resist material, which will help a breakthrough of semiconductor devices for "the internet of things".