This paper presents a novel Vacuum Ultraviolet (VUV) bandpass photon-counting detector which was designed to count photons with energies approximately 9.70 eV for inverse photoemission spectroscopy experiments. The performance was analyzed to improve the signal-to-noise ratio and resolution of the spectrum. The geometric structure of this detector is similar to a special Geiger-Müller tube. It is filled with a dilute mixture of acetone vapor and argon gas. The proportion was investigated and ascertained to be close to 1 to 20. A SrF2 crystal was used as the input window to cut off high-energy photons with energies greater than 9.7 eV. Acetone vapor was selected as the functional gas to capture photons. Moreover, it can prevent low energy photons from being detected. The optical bandpass width is less than 100 meV and can be tuned continuously by cooling the SrF2 window. The temperature is controlled by a self-developed cryogenic system with accuracy of±0.2 K. The relationship between the detector bandpass width and the SrF2 window temperature is calibrated using a deuterium lamp and a grating monochromator.