Abstract: Stem sap flow velocities of Larix sibirica and Betula pendula were measured by using thermal dissipation probe method on sunny side and shade side.At the same time, the correlation between meteorological factors and the stem sap flow of two tree species was analyzed according to the related environmental factors that include photosynthetically active radiation (PAR), air temperature (T), ralative air humidity (RH), saturation vapour pressure and wind velocity were recorded continuously by using automatic weather station. The results were as follows: the diurnal variation of stem sap flow on Larix sibirica and Betula pendula displayed a typical singlepeaked curve in the sunny side and the shade side, the sunny side was higher than that of the shade side. The variation range of Larix sibirica was higher than Betula pendula. During the growing season, the monthly average of stem sap flow for Larix sibirica showed decrease tendency with its maximum appearing in June and minimum in September. The monthly average of stem sap flow for Betula pendula on the sunny side was firstly increased and then decreased, with its maximum appearing in August and minimum in June. The monthly average of stem sap flow for Betula pendula on the shade side showed increase tendency, with its maximum appearing in September and minimum in June. Correlation coefficients declined following the order of air temperature, PAR, RH, wind velocity and saturation vapour pressure. That is, sap flow of the two species were mainly affected by air temperature and photosynthetically active radiation.