To discern the response of soil respiration to heavy rainfall in semi-arid region of the Loess Plateau, soil respiration of wheat field was monitored during three heavy rainfall periods. The first heavy rainfall event happened on May 15, 2005, after a one-month arid period. The soil was in semi-arid state before the second heavy rainfall on May 30. And the soil was wet before the third heavy rainfall which started on July 1 and lasted nearly 3 days. Soil respiration of wheat field was continuously monitored for about 20 days around each rainfall separately (i.e. 10 days before and 10 days after each of the three rainfalls), using three chambers of a multi-channel automated chamber system. Environmental factors were also simultaneously measured. The main factors affecting the soil respiration were selected by stepwise regression method and the relationship between the soil volume water content (SVWC) and soil respiration (SR) was analyzed. The results showed that, (1) Heavy rainfall could both promote and inhibit soil respiration and its effect on SR depended on the soil water state before, during and after the rainfall event. The rainfall promoted the SR when the soil was in arid or water deficit state, but restrained it when the soil was wet. Comparing the values after and before the rain, the SR increased almost 2 and 1.5 times respectively for the first and second rain, but reduced nearly 15% for the third one. The SR reduced 33% during the third rain course. (2) The relationship between the SR and SVWC could be described in a quadratic equation. According to this equation, the inflexion could be considered as a critical SVWC. The SR increased with the increment of SVWC when the SVWC was below the critical value, but decreased with the building up of SVWC when the SVWC was above the critical value. (3)The quadratic relationship was influenced by soil water state and temperature. It was more reliable when the soil changed from arid or water deficit state to soil wet state due to rainfall than that from wet to wetter. On the other hand, the inflexion of the quadratic equation increased with temperature when the soil changed from water deficit state to superfluous state. (4) Temperature and SVWC were interdependent in their effects on SR, and the effects depended on the soil water state before the rainfall. The SVWC was the most influencing factor when the soil was in arid or semiarid state before rain, but its effect on soil respiration weakened and the temperature became the most influencing factor when the soil was enough wet before rain.