Abstract: In-situ fibrous composite foamed material is one type of foams, which is based on in-situ micro fibrillation (IMF) composites and microcellular foaming technology. In addition to the performance of traditional foamed materials such as light weight, shock absorption, insulation, noise reduction, etc., the presence of fiber network structure constructed in IMF composite can significantly improve the microcellular foaming ability of the matrix. Leading to the in-situ fibrous composite foamed material is a kind of new foam with high strength and functionality. This paper first summarized the fabrication process of IMF composites and regulatory factors. The influence of IMF network structure on the crystallization and rheological behaviors were emphatically analyzed. Then reviewed the preparation and pore structure regulation methods of in-situ fibrous composite foamed materials for various IMF composites and microcellular foaming process. The mechanism of strong mechanical properties and application in the field of heat insulation and oil-water separation were then elaborated and listed. Finally, looking forward to the future research directions of in-situ fibrous composite foamed materials.