Abstract: The aim of this study is to clarify the nutrient change rules of nitrogen, phosphorus and potassium in cassava stalk cultivation substrate, so as to provide a scientific basis for the popularization and application of cassava stalk cultivation substrate and nutrient control in organic substrate cultivation. Under the condition of no adding exogenous nutrient, the change rules of nitrogen, phosphorus, potassium, pH value and EC value of cassava stalk substrate at different growth stages of tomato were compared under two conditions of planting tomato and no planting tomato by pot method. During the whole growth period of tomato, the cassava stalk substrate pH value was 7.28-7.86, and the EC value was 3.28-1432 μs/cm, both pH value and EC value conformed to the requirements of cultivation substrate. The changes of total nitrogen and alkaline hydrolysis nitrogen were“down- up- down”. The contents of total phosphorus and available phosphorus showed an increased trend. Before tomato seedling stage, the contents of total potassium and available potassium decreased rapidly due to leaching, but they kept a stable level after tomato seedling stage. The nutrient change rules of nitrogen, phosphorus and potassium in“cassava stalk cultivation substrate + tomato”were similar to the nutrient change rules of“cassava stalk cultivation substrate”. The nutrient contents of nitrogen, phosphorus and potassium with the two treatments were almost at the same level. The seasonal tomato adsorbed few nutrient of nitrogen, phosphorus and potassium from cassava stalk cultivation substrate. Therefore, when we cultivate plants in cassava stalk cultivation substrate, we must supply fertilizer in time to ensure the healthy growth of plants.