Abstract: 【Objective】The influential factors of standing trees internal moisture content variety were investigated. The variety law of moisture content(MC)in different environmental temperature was studied.【Method】In different outdoor temperatures(between-26～10 ℃), time domain reflectometer(TDR)instrument was employed to test Larix gmelinii and Populus simonii tree specimens. The continuous change of temperature and electromagnetic wave propagation time in the tree were then obtained, which were used to deduce the MC of standing trees under different temperature. Based on these, the diurnal variation of propagation time and MC of standing trees were analyzed, and then their variety law in a long time period was further discussed. Finally the quantitative relationship between environmental temperature and MC was determined. 【Result】In one night and day period, the changing trend of MC were basically the same with the internal temperature of tree. With the decline of the daily average tree temperature, the variation range of MC decreased. The average propagation time and MC of the sample trees decreased with the decline of daily average tree temperature. There was no obvious inflection point in the propagation time curve of Larix gmelinii, and the change rate of MC curve was large before -6.3 ℃(14.75%/℃)then tended to be stable(0.94%/℃).The change of Populus simonii was similar to it. There was a significant linear positive correlation between tree temperature and environmental temperature. The fitting goodness of their linear model was higher(R²=0.91). Thus it's feasible to evaluate tree temperature using environmental temperature. The relationship between tree temperature and MC could be divided into three stages. Their relationship at each stage was described as linear models, their coefficient of determination of R² were higher than 0.71. 【Conclusion】Low temperature environment, at environmental temperature as the research point the stocking internal electromagnetic wave propagation time and moisture content change is possible, through the related formula could be deduced the standing trees internal MC.