To investigate the response of transpiration characteristics of Betula platyphylla secondary forest to influencing factors in permafrost area,and to provide scientific reference for accurate assessment of the hydrological effects of forest ecosystems in this region.The sap flow of Betula platyphylla was measured using thermal dissipation probes from May to September 2021 in permafrost area,and the influence factors were observed simultaneously.The results showed that the stand transpiration of Betula platyphylla secondary forest showed obvious hourly,daily and monthly changes during the study period.(1) The hourly transpiration characteristics of Betula platyphylla secondary forest was exhibited that dominant trees > intermediate trees > suppressed trees.Furthermore,diurnal variations of daily transpiration performed a single peak curve pattern in sunny days,while the bimodal curve was observed in rainy days.Meanwhile,the daily mean stand transpiration of Betula platyphylla secondary forest was 1.47 mm/d,with the maximum value appeared in July.A significant monthly variation of transpiration was found during the whole observation period and ranked as follows:July > June > August > September > May,which was 65.08,62.43,54.27,22.92 and 19.84 mm,respectively.(2) The cumulative transpiration of the stand was 224.54 mm,accounting for 32.41% of the total precipitation over the same period,and the transpiration of the dominant trees was the main contributors to the stand transpiration,accounting for 62.64% of the stand transpiration.(3) At the hourly scale,transpiration was mainly affected by air temperature and vapor pressure deficit.At the daily scale,transpiration was positively correlation with potential evapotranspiration,air temperature,solar radiation,vapor pressure deficit,leaf area index and soil temperature (p<0.01),which was significant negative correlation with air relative humidity (p<0.01) and no significant correlation with soil water content (p>0.05),and potential evapotranspiration,leaf area index,vapor pressure deficit and air temperature were the main factors driving the daily stand transpiration.At the monthly scale,air temperature had the greatest impact on stand transpiration,which explained 93.90% of stand transpiration.