A method for adjusting telescopic water pipe and its structure comprise assembling an internal pipe and an external pipe to form a first water passage and a second external water passage, and an independent second internal water passage. A water passage control switch is disposed to an end of the external pipe and has a channel seal cap that divided into a first channel and a first through hole to connect the first water passage. A water stop plug ring is fit to the first through hole. A second and third through holes corresponding to a second and third channels can be connected to the second internal water passage. A rotary switch is connected to the channel seal cap. A penetration hole is disposed to a partition attached to the channel seal cap. An interconnection groove and an arc plane are disposed to the partition.