In order to study the reasonable value of the bottom column end moment amplification factor of the RC frame structure and the rationality of the value of this factor according to the current codes, six RC frame structure models were designed with various column end moment amplification factors and fortification intensity.The models were analyzed based on incremental dynamic analysis by inputting 10 seismic waves to obtain the IDA curves of the structures. On the basis of the IDA, different intensity levels were defined, and the fragility curves and the failure probability of collapse of each structure were obtained. The results shows that the RC frame structure at 7 or 8 degree fortification in accordance with the current codes can satisfy the fortification reqirements for "No Collapsing in the Strong Earthquake"; when the values of column end moment amplification factor and the beam column joint are raised to 1.5 and 1.7 respectively, the probability of collapse under the large earthquakes will be acceptable.