The invention discloses a steel column internally provided with stainless steel downpipes and an installing method of the steel column. The steel column comprises steel pipe columns and the stainless steel downpipes arranged in the steel pipe columns. Long lug plates are arranged at the segmented joints of the steel pipe columns, and fixed butt joint is achieved through the long lug plates. Stainless steel downpipe branch pipes perpendicular to the stainless steel downpipes are arranged at the bottoms of the stainless steel downpipes. The two ends of each stainless steel downpipe branch pipe penetrate out of the side wall of the corresponding steel pipe column and lead outwards, and a steel pipe sleeve is arranged between each stainless steel downpipe branch pipe and the corresponding steel pipe column. Limiting sleeves are arranged on the tops of the steel pipe columns. The stainless steel downpipes are located in the limiting sleeves, and insulating sleeves are arranged between the stainless steel downpipes and the limiting sleeves. The steel column is reasonable in structural design. According to the installing method, the double butt joint hollow long lug plates are adopted for fixing the external steel pipe columns, butt joint of the internal downpipes is conducted, then installing of the steel pipe columns in a butt joint manner is carried out, the installing method is simple and orderly, and joint treatment is simple; and the overall effect is good, and the construction period is short.