A suspension-weighing lysimeter was developed with weighing capacity of 100kg in order to study the evapotranspiration of the potted plants conveniently and effectively. The method of integration and optimization between slave microcontroller and host computer were used. The lysimeter was mainly composed of six parts, weighing sensor, slave microcontroller, host computer, adapting pieces, stand and plant pot. Slave microcontroller of lysimeter includes a microcontroller, data collection and display modules, real time clock, storage module, communication and power modules. The circuits for these parts were designed. Performance tests showed that without human supervision, the slave microcontroller was able to automatically collect, display, store and communicate data through serial interface to the host computer and then the host computer displayed, stored and analyzed the transmitted data. The results showed that the absolute and maximum relative error of lysimeter were 100g and 0.50%, respectively. The ET results of potted plant obtained with the instrument were proved well matched with their actual ET of potted plants with time. It could meet with the requirements of convenience, high accuracy and real time in ET measurement.