The invention discloses a fast imaging type tunnel sky ratio measurement method, and relates to a fast imaging device and a computer which are connected with each other and mounted in a vehicle. The method comprises the following steps: in the vehicle driving process, the using fast imaging is used for performing continuous imaging on a tunnel entrance, and collected pictures are stored in the computer; the computer is used to obtain sky ratio data of the tunnel entrance through the image processing technology. The method has the advantages that the measurement method is simple; quick on-site measurement of the tunnel sky ratio is realized through a digital imaging technology; the scenes of the tunnel entrance can be directly and quickly shot continuously in the vehicle driving process, and continuously recorded range information and sky ratio data can be obtained from the pictures, so that problems in traffic jam and testing safety caused by measurement after a tunnel is closed, are solved, the on-site measurement time is greatly shortened, the on-site measurement cost is greatly reduced, and great convenience is brought to tunnel workers.