We tried modeling of ammonia slip catalyst (ASC) for the purpose of model-based development of urea SCR system which is NOx purification device for diesel exhaust gas. In this report, the practical one-dimensional dual-layer ASC model is developed. This model is made by adding a correction factor to gas adsorption reaction parameters of the previously reported mixed catalyst model. As a result, this model can predict product selectivity of dual-layer ASC in different SCR and PGM washcoat loadings. This model is more practical than previous ASC model and is expected to contribute to efficiency of model-based development.