With the development of Internet of Things and cloud computing, smart home system is gradually rising. Environmental monitoring can be said to be an integral part of the smart home system, in order to facilitate users to monitor the indoor environmental quality in real time, to achieve online environmental monitoring so as to achieve remote monitoring and control, an indoor environmental monitoring system based on Internet of Things technology is designed. The system uses AT89C52 as the central processing unit of the system, and uses DHT11 temperature and humidity sensor, light intensity sensor module and MQ-7 gas sensor to form the data collection node of the system, and transmits the data signal of the collected environmental parameters to upload the data to the cloud server. We use App Inventor to complete the design of the upper computer software, connect to the cloud server, and finally present the data on the mobile App side. Users can view the indoor environmental status information in real time through the mobile phone, and can control the switch of the indoor desk lamp through the mobile App.