This paper presents a detailed technical description of features added to the standard ORANI model to construct a CGE for Sri Lanka, namely, ORANI- SL. The model distinguishes between rain-fed and irrigated agricultural land and introduces water as a production factor. In addition, the new production structure offers the option of substitution between rain-fed and irrigated agricultural lands. The paper also describes the model's database and the steps of the data transformation process from the latest available input-output table of Sri Lanka to the ORANI-SL database, which is necessary for model simulation. The new model could be used to analyse the economy wide impacts of climate change in Sri Lanka, study the economic implications of increased irrigation capacity or sustainable water usage in Sri Lanka, and evaluate the efficacy of various other adaptive strategies to cope with the impacts of climate change. In addition this model can be easily adapted to another country.