Onehealth, an evidence-based decision-making software, is based on the United Nations' epidemiological reference modules to predict the effect of health services. Onehealth is a large database. The software is using activitybased costing, simulating investment costs of health system and changes of mortality in different coverage levels. By the cost of inputs/avoid deaths, it could quantify the cost of health services effectiveness and provide an intuitive basis for the rational allocation of health resources. This study introduces the relevant concepts, model structures and applications of Onehealth. We took the study of child nutrition interventions in Sudan for example and to present Onehealth tool's operating. As a new auxiliary and evidence-based decision-making software with scientific and rigorous theoretical approach, Onehealth has practical significance on the national or regional macro decision-making.