The author generally uses pine, bamboo and plum to express his ideal character and spiritual pursuit. The indomitable pine and cypress, colorful bamboo and winter plum, although belonging to different families and genera, all have noble styles that are not afraid of severe frost. They lived together in the cold of the old days, and they have always been admired by China ancient and modern literati, and they are called "three friends in the cold of the old days", which is a metaphor for loyal friendship.