Infrared thermal imaging， which measures the surface temperature by detecting infrared radiation （IR） spontaneously emitted by the object itself， is widely used in important fields such as military， civil aviation， security monitoring， and industrial manufacturing. However， due to the diffraction limit， the spatial resolution of IR thermal imaging is usually above the micron scale and cannot be used to image nanoscale objects. In recent years， we have developed a passive-type infrared near-field （NF） microscopy. It detects the NF radiation exists on the sample surface and therefore achieves high spatial resolution well-below the diffraction limit. In this paper， we introduce the construction and detailed mechanism of this novel microscope and recently achieved research progress， i.e.， sensitive detection of NF radiation and super-high resolution infrared temperature mapping of working devices.