Heat transfer tubes for evaporators in air conditioning and refrigeration systems, each tube including: a tube body (1); outer fins (2) extending on an outer wall surface of the tube body (1) and having outer fin walls opposite to the outer fin walls of the adjacent outer fins; channels (6) located between the adjacent fins (2) so as to constitute channel chambers; fin top platforms (3) on respective tops of the outer fins (2), the fin top platforms (3) including fin top edges (3a) extending from both sides of the fin top platforms (3) so that the channel chambers form a cavity structure as a whole; channel chamber openings constituted by gaps between the adjacent fin top edges (3a) of the fin top platforms (3) of the outer fins; and lateral fins (4) arranged on portions or substantially middle portions of the outer fin walls of the outer fins (2) in a height direction of the outer fins (2) and at intervals in an spreading direction of the outer fins (2), so that the cavity structure is formed into a double cavity structure.