Abstract: The assembly exchanging reactivity worth is defined as the reactivity change when the assembly of a core position is replaced by a relative one. The measurement test program and process of the CEFR assembly exchanging reactivity were described. There were 8 typical positions totally in this test. Separately, fuel assemblies of six positions were replaced by stainless steel assemblies, and other stainless steel assemblies of two positions were replaced by fuel assemblies separately. The measurement results show that the worth of the assembly exchanging reactivity of fuel positions reduced from -980 pcm (inside of core) to -470 pcm (outside of core). The theoretical calculation of the testing program was carried out using the CITATION code. The calculation results were in good agreement with the experimental values, and the comparison inspected the engineering practicality of the CITATION code.