The diode microbolometer uncooled IRFPAs (infrared focal plane arrays, IRFPAs) have shown broad prospects in recent years. The performance of the IRFPAs is limited by sources of noise from the detector itself which must be further studied and decreased to achieve better performance. This paper outlines sources of noise from the detector, quantifies the RMS (root-mean-square, RMS) noise voltages from different noise sources, discusses their implications and finally obtains performance limits of the diode microbolometer IRFPA. Moreover, the optimum structural parameters are also studied. The theoretical computation results show that the temperature fluctuation noise-limited NETD (noise-equivalent temperature difference, NETD) of the detector is 2.36mK with a corresponding radiation-limited conductance of 2.06 nW/K. In addition, the optimum NETD of 46.5 mK can be obtained when the detector operates in the forward bias current of 33 μA and the ratio of temperature sensing area is 54% in a 25 μm×25 μm micromachined structure.