The working principle leads long period fiber grating (LPFG) more sensitive than fiber Bragg grating (FBG) in sensing areas such as temperature, strain, concentration, bending etc.. LPFG has great potential in the field of sensors. Compared with FBG sensing signal, the signal interrogation of LPFG needs further research to satisfy the LPFG sensing application. The signal interrogation techniques of LPFG are reviewed and analyzed. The methods of using edge-filter, Fabry-Perot (F-P) cavity and arrayed waveguide grating (AWG) to interrogate LPFG sensing signal are analyzed and compared particularly. The approach to interrogate multiplexed sensors based on LPFG is introduced. Summary and expectation of demodulation technique development trend are presented.