A channel mixer includes a substrate, a channel assembly, and a pressing assembly. The channel assembly is located on the substrate and has at least one channel, a first opening for accommodating at least two testing materials, and a second opening. Two ends of the channel are respectively communicated with the first opening and the second opening. The pressing assembly covers the second opening and has an air chamber communicated with the second opening. When the pressing assembly recovers to an initial position after been pressed and released, the air chamber generates a negative pressure to draw the testing materials in the first opening therein, such that the testing materials are moved toward the second opening along the channel and mixed with each other.