Based on the environmental conditions where this disease is prone to occur, this technology analyzes with reference to disease occurrence records of the cultivation field, establishes a calculation model of an early warning system, and imports the meteorological forecast data and observation records into the system. This can provide early warning of the risk degree of lettuce leaf spot disease occurrence, and suggest the timing of prevention and treatment, to achieve the goal of precise fungicide use. This not only can reduce the risk of disease damage, but also decrease the frequency and amount of treatment, and further reduce carbon emissions by 3.8791 (kgCO2e/ha) during the cultivation process.