Abstract: Interferograms of laser-induced epoxy fiber reinforced polymer plasmas are obtained through a Mach-Zehnder interferometry system. An improved digital double-exposure Fourier method is applied to extract initial wrapped phases from interferograms, and then an improved phase unwrapping algorithm based on a mask and a branch-cut method is proposed to solve the problem of phase unwrapping. After the inverse Abel transformation of the unwrapped phase, spatial distributions of the electron density of laser-induced epoxy fiber reinforced polymer plasma at various delays are acquired. Results show that the measured electron density of the plasma is mainly distributed on the order of 1018 cm-3. The experiment also indicates that the total amount of laser plasma electrons changes slightly within the recorded time and the change of the electron density is approximately inversely proportional to the change of the plasma volume.