The combined effect of nitrogen (N) addition, temperature change and crushing on the decomposition of soil organic carbon (SOC) is still poorly understood. A short-term incubation experiment was conducted to investigate this problem using soils from a freshwater marsh in Sanjiang Plain, Northeast China. Our results showed that increase in temperature promoted SOC decomposition, whereas nitrogen addition inhibited SOC decomposition. Crushing produced varied effect on SOC decomposition: changing from positive to neutral as temperature increasing. The suppressing effects from N addition was weaker than stimulating effect from a 10 degrees C increase in temperature on SOC decomposition, leading to a positive effect on SOC decomposition from N addition and temperature change. Combined effect of N addition and crushing on SOC decomposition varied from promotion to inhibition following increase in temperature. The combined effects of nitrogen addition and temperature, crushing and temperature, and the combined effect of these three factors on SOC decomposition were antagonistic, whereas the combined effect of N addition and crushing on SOC decomposition was additive. Both N addition and crushing decreased the temperature sensitivity of SOC decomposition.