Electrospinning method uses electrical force to produce a polymer nanofiber from a polymer solution. The surface morphology and the pore formation of e-spun fiber have been studied by many variables that are involved in different polymer concentrations and solvent mixing ratios. Another major factor affecting fiber morphology and size distribution is the relative humidity. The interaction between the relative humidity and the solvent evaporation affects the distribution of electric charge on the surface of the e-spun fiber. The higher the electric density, the thinner the fiber that can be produced in low humidity conditions. The relative humidity and solvent evaporation can create pores on the fiber surface. The pores can be formed under the condition of 30% relative humidity using 100% of THF solvent. The boundary of the pores has expanded and becomes formless due to the agglomeration of each pore, which can decrease the evaporating capacity.