The background pictures of many infrared focal plane arrays which are poor in capability, often come forth some invalidated phenomena which are just like “black line”,“sawtooth”, “blob round” and etc. The reason may be that the infrared detector has some defects or the readout circuit exist some problems. The problems which may exist in the IRFPAs are equal to invalidated model. Then with the EDA software, this work simulated the invalidated IRFPA which is using DI and CTIA readout mode. By simulating and emulating the signals of the IRFPAs which is 3×3 and 10×10, this work analyzed the reasons of invalidated phenomena in the background pictures. The results of simulating the signals of the invalidated IRFPAs, give the referenced gist for improving the IRFPAs readout circuit.