Real-time and comprehensive monitoring of environmental information in agricultural fields can help farmers keep abreast of the field crop growth environment and fertility， and provide valuable information for farmland irrigation， crop growth modeling， and pest and disease prediction. In order to meet the actual requirements of agricultural environmental monitoring， a real-time monitoring system for multiple environmental parameters in agricultural fields based on narrow band internet of things （NB-IoT） has been developed according to the requirements of environmental parameter monitoring indexes stipulated in national standards and local standards and so on. Eight key environmental parameters such as air temperature， relative humidity， CO₂ concentration， illuminance， soil humidity， soil temperature， pH and electric conductivity (EC） are monitored in real time. The sensor nodes are deployed in the farmland field to monitor environmental data in real-time， and wirelessly transmit the data to the OneNET cloud platform via NB-IoT base stations. Growers can access the cloud platform via cell phones or computers to obtain relevant environmental data for agricultural fields. The experimental results show that the system can realize accurate acquisition and remote transmission of environmental parameters， and can meet the real-time monitoring requirements of the actual agricultural field environment. The system， if widely popularized， can significantly improve the environmental monitoring for agricultural fields and the agricultural production efficiency.