Dynamic spectrum (DS) can be used to eliminate the individual discrepancy of tissues theoretically except the pulsatile component of the artery blood (PCAB). One of the systematic errors in the calculation of the component changes from NIRS data of the dynamic spectrum is the absolute magnitudes and relative differences in path-length factors as a function of wavelength. Monte Carlo simulations are used in the present paper to examine the importance and mitigation methods of this error while the photoelectric pulse wave is detected on the finger tip. The measure accuracy of the DS method is evaluated by error analysis.