1. In the plan phase, includes four steps, namely, to find out the existing problems, analyze the causes of the problems, find out the main reasons, and formulate countermeasures.
2. Do (do) stage: implement according to the formulated countermeasures and collect corresponding data.
3. Check (check) stage: check the effect obtained, evaluate the effect of improvement, and see if the actual result is consistent with the original goal.
4. Aact stage: It consists of two steps: namely formulating consolidation measures to prevent problems; proposing remaining problems and the next step.