Rail Rolling Contact Fatigue (RCF) crack is one of the main reasons affecting the safety and comfort of rail transit operation. In order to further quantitative estimate rail RCF crack morphology parameters, the calculation model of rail-crack-air electromagnetic excitation and response is established by using the method of alternative current field measurement (ACFM) and the field testing results of rail RCF crack. The response of ACFM to crack parameters is calculated and analyzed. A method for estimating crack internal parameters is proposed based on linear interpolation and cubic spline interpolation. The rail RCF test platform based on function wave signal generator, lock-in amplifier and digital signal acquisition instrument is built. An ACFM excitation-measuring probe is prepared based on U-shape core, excitation coil and detection coil. According to the field observation results of rail RCF crack, the machining and experimental testing of rail RCF cracks are conducted. Through simulation and experiment test, the built ACFM response model and the internal parameters estimation method are verified. The built calculation model, experimental platform and crack parameters estimation method in this study lay a foundation for further quantitative detection of rail RCF crack.