Aiming to solve the problem that plant water physiological information (plant water and ice content) during freeze-thaw process is difficult to be monitored on-line and continuously in real time and judged accurately by freeze-thaw process. A monitoring sensor for freeze-thaw of living standing trees was designed based on latent heat effect, which detected the temperature caused by latent heat release during plant freeze-thaw process. Based on the accurate detection of freeze-thaw point, the ice content and radial freeze-thaw depth of stem volume during freeze-thaw process were calculated according to the change of moisture content of stem volume. At the same time, a circular projectile probe was designed to eliminate the pressure of fixed probe on stem to form a groove. Calibration results showed that the determination coefficient of fitting between the measured results and the true values of the sensor was more than 0.99. Static and dynamic characteristics showed that the measurement range of moisture and temperature of the sensor was from 0 to 68.67% and -30℃ to 80℃, respectively, and the dynamic response time was less than 2 s. The results of indoor freezethaw simulation experiment and outdoor long-term freeze-thaw monitoring showed that the sensor can effectively detect the changes of water physiological information during plant freeze-thaw process. It provided a device with independent intellectual property rights, realtime continuous monitoring, low cost and easy installation for agricultural and forestry production and plant freeze-thaw assessment.