An unbonded type of gauge device was developed for continuous measurement of changes in stem diameter. The study was undertaken to examine the temperature drift of the device under different temperature conditions (8.8 to 36.8°C) and to determine its resolution of changes in tomato stem diameter for 3 days. The current data indicate that the temperature drift of the system was only 3μm for 10°C change and also that the changes in tomato stem diameter could be monitored continuously with high sensitivity with an error ranging from 2.1% to 3.5%. These results suggest that the method ensures to diagnose effect of temperature on tomato plant growth status at real time.