This utility model discloses a real-time PCR instrument adapted to the placement of test tubes of different sizes. It relates to the technical field of real-time PCR instrument equipment. The instrument includes a main body with a mounting mechanism for
test tube detection. The mounting mechanism includes a lifting component and a detection box connected to the main body via a sliding component. Test tubes of different sizes are inserted from top to bottom into a hole composed of a positioning ring and an arc-shaped ring. When the outer wall of the
test tube contacts and presses downward against the positioning ring, the positioning ring compresses a spring, causing it to move. The spring's rebound force is converted into a uniform and gentle radial clamping force on the outer wall of the
test tube, thus initially adapting to and holding the test tube, achieving initial positioning. The positioning force can automatically adjust according to the size of the test tube, achieving good positioning for test tubes of different diameters, improving the instrument's adaptability to test tubes of different specifications.