A connecting and adjusting structure for a crank assembly used in a bicycle contains a first tube of a first connector including a first hollow portion, the first connector including a first bearing seat to receive a first ball bearing, the first bearing seat includes a first engaging tab, a first adjusting rib, and the first tube, a second connector including a second bearing seat to receive a second ball bearing, a dustproof cover, and a retaining ring, the second bearing seat including a second engaging tab, a second adjusting rib, and a second tube, a second crank including a central shank with plural T-shaped teeth and second internal screws, a first crank including a hollow post with a Tee groove fixed to engage with the T-shaped teeth, and a screw is inserted through the hollow post to be screwed with the second internal screws.