Christmas tree is a kind of wellhead assembly consisting of triple valves, four way valves and apparatus, which is used for the fluid control of oil and gas well, provides the inlet for production flow columns. Different kinds of combination could be made by Christmas tree assembly, to satisfy any special need. By various purposes, Christmas tree could be classified with such special wellhead assembly as oil-extraction (natural flow, artificial lift), gas production (natural gas and all kinds of acid gas), water flooding, thermal extraction, compressive fracture, acidification and so on. And it can be partitioned into different series according to different pressure grades.