Soil is an important source of atmospheric carbon dioxide (CO₂). It is an important process for soil respiration to release CO₂ from biosphere to air, because understanding the rate of soil respiration and temporal and spatial fluctuation under various terrestrial ecosystem can provide the basic data to budget of global carbon balance and to estimate potential effect of global change. Soil respiration was not only influenced by environmental conditions such as temperature, humidity, and pH values, but also was controlled by biotic factors such as vegetation form, leaf area index, living weight and human reactivity. It is noted that soil temperature and moisture content are assumed to two significant environmental factors. Loess plateau located in semiarid districts of northwest of China, where soil exhibited dry and humid change alternately. Studies of CO₂ emission from bare soil may help analyze annual changes in carbon (C) in soil organic matter (SOM). Therefore, CO₂ emission associated with the decomposition of SOM from bare soil are important factors for assessing the C budget in agricultural fields. Studies on relationship of soil respiration change and environmental factors (soil temperature and moisture content) presented the important significance to determine the temporal and spatial change of soil respiration in this bare area. We conducted a study to monitor soil CO₂ emission diurnal change, CO₂ emission seasonal change, soil moisture, soil temperature, and assess the controlling factors of CO₂ emission from an unplanted soil of long-term experiment at Changwu ecological station of Chinese Academy of Science, China. In situ soil CO₂ emissions from March 2008 to March 2009were measured with an IRGA CO₂ analyzer (Li-COR 8100, Li-COR Corp., Lincoln, NE) following the dynamic closed chamber method. The CO₂ diurnal and seasonal change in the bare soil followed single peak trend, same as the change of soil temperature. The highest value of diurnal change appeared at 14:00 or 16:00, and the lowest value appeared at 0:00 or 6:00. The CO₂ flux increased in summer and decreased in winter. The average of CO₂ emission during the study period was 0.9μmolCO₂·m^-2·s^-1. There were significant positive correlations between the CO₂ flux and soil temperature (P<0.01). The regression equation of R_s=ae^bT fit the relationship between the CO₂ flux and soil temperature very well, especially in 0-5 cm soil depth. Unlike soil temperature, apparent relationships between CO₂ flux and soil moisture were not observed. Bi-variable model R_s=ae^bTW with soil temperature (T) and soil moisture (W) could explain variation of soil respiration much better than mono-variable model.