The present invention discloses an optical system axial parameter measurement device and method. The device comprises: a low-coherence measurement unit, a high-coherence scale unit, a scanning unit, ameasuring range multiplication unit and a signal processing unit. The low-coherence measurement unit is configured to generate low-coherence interference waves; the high-coherence scale unit is configured to generate high-coherence interference waves; low-coherence reference light and high-coherence measurement light pass through the scanning unit; the scanning unit is configured to provide the same optical delay line for the low-coherence interference waves and the high-coherence interference waves; the measuring range multiplication unit is configured to collect the low-coherence interference waves generated by the low-coherence measurement unit and enlarge a measuring range; and the signal processing unit is configured to take the high-coherence interference waves as a reference datumto perform analysis processing of the low-coherence interference waves collected by the measuring range multiplication unit and obtain axial distances between dielectric interfaces of the optical system. The optical system axial parameter measurement device and method is large in measurement range, high in signal to noise ratio and rapid and accurate in measurement.