The air quality monitoring and early warning system based on the Internet of Things cloud platform can be used to reflect the indoor air quality status and issue warning information to users in a timely manner. The system consists of four parts: air quality index data acquisition end, OneNET cloud platform, data visualization web page and small program early warning end. Air quality index data acquisition terminal: the acquisition terminal uses STM32F103C8T6 as the main control core, and uses DHT11 temperature and humidity sensor, MQ-2 smoke sensor, MQ-3 alcohol sensor, MQ-7 carbon monoxide sensor, MQ-135 air quality sensor and PM2.5 sensor (GP2Y1010AU0F) to collect data of seven indexes such as indoor temperature, relative humidity, smoke, alcohol, carbon monoxide, carbon dioxide and PM2.5 respectively, and uses ESP8266-01s connection WiFi to upload the data to OneNET cloud platform. OneNET cloud platform: OneNET cloud platform is used to store the data uploaded by the data collection end, so that the data visualization web page and WeChat applet can obtain data from it. Data visualization web page: includes functions such as data viewing and historical data statistical charts to visualize data on web pages. Small program early warning end: including information view and alert threshold two parts. The user can set the threshold, and when the actual indoor air pollution index exceeds the set threshold, the system pushes the warning message to the user and reminds the user to pay attention to the protection.