The model of thermodynamic analysis coupling with radioactive resource compute in condition of small-break LOCA was established. The radioactive result of the reactor cabin for different break size was analyzed and investigated using developed software of Source Radioactive Compute for Nuclear Reactor (NSRC). The radioactive effect had been evaluated in both conditions of cold leg and hot leg safety injections. The results show that the break inch, safety injection position and the isolation time of break can influence the radioactivity of reactor cabin directly, which may give some suggestion for the inspection of radioactivity and treatment of the design basis accident with different size small-break LOCA.Cited