In this study, an analytical model based on the equivalent circuit method is developed to simulate the frequency response of an insert earphone. This earphone incorporates a miniature loudspeaker commonly used in computer, communication, consumer, and car electronics. Through the laser triangulation method, electroacoustic parameters of a miniature loudspeaker are obtained. Several earphone design configurations are analyzed in accordance with the open and closed states of front leakage hole, vent, and back leakage hole. To validate the analysis, an insert earphone that is attached to IEC-60711 coupler and a specially designed fixture tube is experimentally measured for frequency response using electroacoustic equipment in the air. Simulation and experimental results show good agreement over the complete audible frequency range. Analysis indicates that states of front leakage hole, vent, and back leakage hole of an insert earphone have significant effects on frequency response. The front leakage hole affects the low frequency response, whereas the vent affects the fundamental resonance. Detailed analysis has been provided to further improve the design of insert earphones.