The silicon-on-insulator(SOI) diode uncooled infrared focal plane array(IR FPA) uses single-crystal silicon PN junction diodes as a temperature sensor, and has various advantages over other MEMS-based uncooled IR FPAs. The basic principle and the advances of the two different SOI diode uncooled IR FPA are describes, including operation of the diode temperature sensor, the design of the pixel structure, the theory calculation and the simulation results. The improved structure, the IR absorbing structure was made in the upper level to cover almost the entire pixel area, in which the fill factor can increase from 21% to 80%. The calculated results show that the sensitivity of the improved structure raises to 7.75×10-3V/K and the noise equivalent temperature difference(NETD) decreases to 43mK(f/1.0) in a 35μm×35μm micromachined structure, which is close to the international advanced level. Meanwhile, the simulation results also confirm the improved performance and the possibility for large format uncooled IR FPAs.