Changji, a Miao nationality double-reed air-sounding instrument, consists of two juxtaposed pipes. "Changji" in Miao language means a pair of wind instruments. The Han people call it double-pipe. Can be played solo, ensemble or accompaniment. Popular in Guangxi Zhuang Autonomous Region, Guixi Longlin Autonomous County, Bianya and other Miao inhabited areas.

The double tube of Changji is made of two bamboo tubes of the same size and length bundled side by side. Each tube is equipped with a core and a whistle, and has a common gas card.

The tube body is made of bamboo, mostly made of thin bamboo tubes with bamboo joints at the beginning, the lower end is open, and the middle is transparent. The specifications and sizes are different, the common ones are 28 cm in length, 1 cm in outer diameter and 0.7 cm in inner diameter. The left tube has eight (seven in the front and one behind) circular sound holes, of which the back hole is between the sixth and seventh holes, and there are six circular sound holes on the front of the right tube, except for the back of the left tube. Outside the holes, the pitch of each sound hole is equal, and the positions of holes 1 to 6 of the left and right pipes are the same.

Bamboo joints are left at the head end of each tube body, and a small round hole with a diameter of 0.6 cm is drilled in the center of the section septum for inserting the core. The core plays the role of connecting the tube body and the whistle. It is mostly made of thin bamboo or goose feather tubes that are thinner than the tube body, 2.5 cm long, 0.6 cm outer diameter, slightly tapered at both ends, and the upper end is used to place the whistle. Insert the lower end into the small round hole of the bamboo joint of the tube head. The left and right cores are put together on a gas card. Qi cards are round slices made of gourd shells, with a diameter of 4 cm and a thickness of about 0.5 cm. They are used to hold the lips when playing, which can help luck and make the mouth last.

The pipe whistle is made of reed pipe, with a length of 1.5 cm and an inner diameter of 0.6 cm. It does not need any processing. It can be used by flattening the whistle with the mouth. The upper and lower ends of the two pipes are firmly tied with ropes.