[Background] Soil respiration ( R_S) is a key step in the carbon cycle of forest ecosystem, which mainly consists of two parts: autotrophic respiration ( R_A) and heterotrophic respiration ( R_H) . The decisive factors of autotrophic and heterotrophic respiration are different. In addition,the heterotrophic and autotrophic components of soil respiration may respond differently to climate change. Our goal is to assess the relationship between soil respiration and soil temperature and humidity,to determine the relative contribution of autotrophic and heterotrophic respiration to soil respiration,and to investigate the effect of continuous cropping on soil respiration and its components. The study site is located in the sandlot along the Dawen River,Shandong Province of eastern China. [Methods]We took different continuous cropping generations of poplar plantation ( i. e. first generation,second generation and third generation) as the research objects. We used a field setup through trenching method to distinguish between heterotrophic and autotrophic respiration,and ACE automatic soil respiration monitoring system to measure the dynamics of soil respiration during the growing season in 2015. Meantime,soil temperature and soil water content at 5 cm depth were also measured by the self-contained temperature and moisture sensor of the instrument mentioned above. We used three empirical models to fit and analyze the relationship between soil respiration,soil temperature and volumetric water content. In addition,the soil bulk density,pH value, soil organic carbon ( SOC) ,total nitrogen ( TN) and microbial biomass carbon ( MBC) content in 0 -20 cm soil depth of three forest types were observed. [Results]1) Soil respiration and its components presented significant monthly variation as unimodal pattern,and were consistent with the change of soil temperature. 2) The average soil respiration rate of three forest types on their growth seasons were 3. 12 mumol /( m~2·s) ,3. 08 mumol /( m~2·s) and 2. 66 mumol /( m~2·s) respectively. R_S and R_H of the third generation forest were significantly lower than that of the first and second generation forest,while R_A showed no significant difference among the three forest types. 3) Contribution rate of R_A of the first generation,second generation,third generation and overall mean value was 39. 39%,38. 47%,42. 25% and 40. 04% respectively,and showed seasonal differences,but the difference alone the three stands was not significant. 4) Soil temperature and volumetric water content were not significant among the three types of forest during the observation period. Soil respiration and its components showed significant exponential relationship with soil temperature in 5 cm depth,and no significant relationship with volumetric water content. The goodness of the binary mixed model indicated that the combined effects of soil temperature and volumetric water content on soil respiration and its components were 80% - 94%. The simulation results showed that the binary mixed model was the best. [Conclusions]In summary,continuous cropping of poplar plantation reduced soil respiration rate and heterotrophic respiration rate,and the difference on soil physical and chemical properties and microbial biomass is the main reason leading to the difference in soil respiration rate alone different stands. This study revealed the effects of continuous cropping on soil respiration and its components,and provided data support for the comprehensive study of continuous cropping effect and soil carbon cycle in poplar plantations.