Electrospinning is a simple, convenient and efficient technique to fabricate continuous nanofibers, which can be applied to the fields of tissue engineering, drug delivery and catalyst loading widely. In recent years, much attention has been paid to electrospun nano-fibers with porous structure due to their ultrahigh specific surface area. Preparation methods and pore forming mechanism of nano-fibers with porous structure were reviewed. The progress and development trend of nano-fibers with porous structure caused by liquid phase separation and solid phase separation were discussed in detail. The interaction between consolidation rate of jets and evaporation rate of solvents was analyzed based on the solvent properties and the experimental conditions, such as miscibility, temperature and humidity. Methods for preparing pore structure controlled nano-fibers by multi-way were also proposed.