The Brillouin spectroscopy technique based on virtual image phased array (VIPA) is a high-resolution spectral detection technique.It offers advantages such as real-time monitoring and high sensitivity.Currently,this technique primarily relies on the mapping relationship between the free spectral range (FSR) of VIPA and the pixel to obtain frequency information.However,variations in the incident light angle can cause fluctuations in the FSR.Traditional measurement methods are based on the assumption of constant FSR and do not provide real-time calibration for FSR changes caused by variations in the incident angle,resulting in measurement errors.In this paper,we address this issue by analyzing the characteristics of Brillouin scattering and the interference principle of VIPA.We propose a real-time calibration method for FSR based on the Brillouin frequency shift of a single-mode fiber and a corresponding calculation method for pixel-to-frequency mapping.This method utilizes the Brillouin Stokes and anti-Stokes frequency shifts of a single-mode fiber as references to reduce frequency measurement errors caused by FSR fluctuations due to changes in the incident light angle.Experimental results demonstrate the rapid measurement of micro/nano fiber Brillouin frequency shift in different refractive index environments at a wavelength of 532 nm using this method.