The invention relates to a construction method of a backfill area foundation pit supporting structure. The construction method comprises the following steps: S1, constructing slope protection piles and top beams; S2, constructing a plurality of pairs of profile steel cement soil mixing piles on the sides, away from a foundation pit to be excavated, of the slope protection piles, wherein each pairof profile steel cement soil mixing piles are arranged at intervals, the multiple pairs of profile steel cement soil mixing piles are connected into a whole through cross beams, and the cross beams are connected with the top beams of the supporting piles in a pulled mode; S3, excavating the foundation pit in a layered mode, and then carrying out anchor rod construction on the side wall of the foundation pit, wherein the tail ends of the anchor rods penetrate through the space between each pair of profile steel cement soil mixing piles, grouting is carried out in anchor rod holes, sectional grouting is adopted, and expanded heads are formed at the ends, extending out of the profile steel cement soil mixing piles, of the anchor rods; and S4, carrying out waist beam construction, and carryingout excavation of a foundation pit of the next layer. The profile steel cement soil mixing piles are arranged behind the slope protection piles, the pulling and fixing effects on the slope protectionpiles are achieved, meanwhile, anchor rod grouting bodies are matched with the profile steel cement soil mixing piles to increase the pulling resistance of the anchor rods, and therefore the stability of pile-anchor supporting is improved.