Like acupuncture Chinese Massage is based on the theory of jing luo or channels and collaterals. According to this theory the body is networked by a system of pathways which function to transport qi and blood, to regulate yin and yang, to protect against external pathogens and to link the internal organs with the exterior. Blockage of the jing luo causes pain and is intimately connected with all health problems.
dredging the channels ( in the sense of removing external pathogens like cold and damp)
regulating qi and blood ( in the sense of dispersing stagnation and guiding counterflow)
activating qi and blood ( in the sense of increasing its activity)
Massage also relaxes the jin ( sometimes mistranslated as tendons, jin actually refers to the function of all soft and connective tissue in relation to movement and flexibility) to ease spasm and increase flexibility and straightens the joints. Both jin and joints closely affect the flow of qi in the jing luo.
What is particularly interesting is that these effects create movement in one form or another. Since in TCM terms pain is simply a lack of free flow of qi and blood, this is why Chinese Massage is such a powerful treatment for pain.