To solve the long detection time in traditional soil nutrient testing, the shortcomings of transmission distance limitation in currently available portable equipment, and the susceptibility to detection precision degradation caused by temperature interference, a cloud-based portable sensor for the detection of basic soil nutrients is introduced in this paper. The sensor uses STM32F407 as the main control chip and employs a 485 type, five-pin, four-parameter soil sensor, which can measure the temperature, moisture, pH value and NPK at the same time, and realizes the data acquisition of the four parameters through the Modbus RTU protocol. The FS-MCore-F800 series highly integrated 4G Cat.1 module is adopted to implement real-time remote transmission of detection data and remote monitoring functions. Through testing, the device offers extensive signal coverage and stable communication under weak signal conditions. It supports integrated detection of multiple sensors via RS-485, while reducing moisture measurement errors through a random forest-based temperature compensation model. The cloud platform enables multi-terminal access, and the device features excellent operability, presenting broad promotion prospects in smart agriculture.