The present invention provides an adjustable optical measuring device and a measuring method which adopts the adjustable optical measuring device for measuring liquid crystal display device. The adjustable optical measuring device comprises a loading substrate, a clamping substrate and a rotation shaft, wherein the loading substrate comprises a containing groove. The clamping substrate comprises astoring cavity corresponding with the containing groove. The loading substrate and the clamping substrate are installed separately with a stacking mode. The rotating shaft is clamped between the loading substrate and the clamping substrate. The measuring device realizes the optical film replacing of liquid crystal display device to be measured through rotation adjustment, simplifies a measuring procedure and effectively increases the measuring efficiency and measuring precision.