A phase-change non-destructive pipe expanding method for an inner finned pipe is disclosed. The method comprises the following steps : bending a copper heat exchange pipe (1) into U shape and removing greasy dirty and oxidized layer on the surface of the copper heat exchange pipe (1); sleeving an aluminum alloy fin group (2) on the copper heat exchange pipe (1) in series, welding all segments of the U-shaped copper heat exchange pipe (1) to obtain a loop, sealing the two ends of the loop, and vacumizing the inside of the loop and pouring a liqu...