The invention discloses a profile steel assembly used for foundation pit supporting. The profile steel assembly is characterized in that the profile steel assembly comprises a profile steel core, a steel casing and a sand resistant device; the profile steel core is arranged in the steel casing; a gap is formed between the steel casing and the profile steel core and filled with sand; and the sand resistant device is used for sand storage or discharging. The defects such as difficult construction, high cost and long construction period of traditional construction methods in the SMW work method construction process are overcome, soil looseness is avoided after pullout, the original structure can be maintained, and the construction difficulty is greatly lowered. The construction progress is accelerated advantageously, and labor and machine cost is reduced. The profile steel core recovery rate is high, the turnover frequency is high, and the economic benefits of projects are increased.