An air purifying prompting system includes an air purifying system and a prompting server wirelessly communicated with the air purifying system. The air purifying system includes an air purifying processor, an air filter communicating with the air purifying processor, a positioning module for positioning the air purifying system, and an air quality sensor for detecting air quality around the air purifying system, wherein the prompting server is arranged to generate an air filter usage time data. The air filter usage time is used to activate generation of air filter prompting signals to the air purifying system.