Abstract:The Stem radius variation (SRV) was measured by dendrometer from six sample trees of Picea meyeri at the tree-line of Luya Mountain, North China, combined with synchronized instrumental observation and measurement of habitat temperature, moisture, etc., from July 15th to the August 7th (summer phase) and from September 5th to October 9th (autumn phase) in 2007. The preliminary analytic results were as follows: (1) the diameter of stems varied on sunny days with a daily fluctuation but steadily widened, while on rainy days it continuously increased during the rain but shrinked rapidly after the rain. (2) The Stem radial increment(SRI) pattern in both phase, was fitted with a conic curve pattern, The SRI was shown a positive value in the summer phase, whereas in the autumn phase, it was turned out to be a negative figure first in early September but then kept as a zero constantly from the middle September on. (3) In no rain stage of both of these phase, the stem radius variation (SRV) was negatively correlated with air temperature and positively correlated with relative humidity (RH), soil moisture and soil water potential. Correlations between SRI and soil temperature were different. Daily stem fluctuation rhythm broken by precipitation correlations of soil temperature and other factors were different in rainy phase of both phases. (4) Through distance analysis, we found that a relative warmer and moister environment was suitable in autumn phase, and high RH and soil moisture was suitable for the growth of Picea meyeri in summer phase.