The invention relates to a femtosecond CARS (coherent anti-stokes Raman scattering) three-dimensional spectral detection system and method for study on molecular superfast dynamics and aims to solve the problems such that the traditional CARS detection system is poor in stability and complex in structure, and the influence of stray light upon signal detection. The system comprises a femtosecond laser, a first time delay unit, a second time delay unit, a third time delay unit, an optical parameter amplifier, a first diaphragm, a second diaphragm, a third diaphragm, a fourth diaphragm, a fifth diaphragm, a first beam splitter, a second beam splitter, a sample pool, a spatial diaphragm, a monochrometer, a photoelectric multiplier tube, a phase-locked amplifier, a first lens, a second lens, a first reflector, a second reflector, a third reflector, a fourth reflector, a fifth reflector, a sixth reflector, a seventh reflector, an eight reflector, a ninth reflector, a tenth reflector, a dichroscope, a computer and an optical chopper. The system and the method are applicable to spectral detection.