The invention provides a shrinkable tube expansion vacuum and external diameter automatic adjusting device. The shrinkable tube expansion vacuum and external diameter automatic adjusting device comprises a diameter measurement device, a controller, a servo motor, a linear motion guide rail and an aperture adjuster. The shrinkable tube expansion vacuum and external diameter automatic adjusting device can obtain data according to real time external diameters of products, makes a comparison between the data and a standard external diameter value, controls the servo motor to rotate and further drives the aperture adjuster to act, can automatically controls the vacuum degree inside the vacuum box body of expansion equipment, meanwhile achieves adjustment to difference of pressure inside and outside a product, achieves adjustment to the external diameter of the product, achieves real time and continuous adjustment to the external diameter of the product, and is convenient for intelligent adjustment during an expansion process, thereby improving the product stability and product quality.