The invention discloses an unpowered gravity ore dressing method. Tailings of a dressing plant are graded by a flushing type hydrocyclone, over flows flow into blanket type chutes automatically, a main ore feeding groove, an ore feeding pipe, an ore separating groove and a plurality of ore separating pipes arranged side by side are arranged at an ore feeding end of each chute; a concentrate ore discharging pipe, a tailing discharging pipe and an ore discharging insertion pipe are arranged at an ore discharging end of the chute; the concentrate ore discharging pipe is communicated with a concentrate ore ditch; the tailing discharging pipe is communicated with a tailing ditch; the chute comprises a first inclined section and a second inclined section which is connected with the first inclined section sequentially from the ore feeding end and the ore discharging end; the width of the second inclined section decreases in an ore discharging direction; the inclination degree of the second inclined section is larger than that of the first inclined section; ore discharging guard plates are arranged on two horizontal sides of the first inclined section and the second inclined section respectively; and communication conversion plugs are arranged on the concentrate ore discharging pipe and the tailing discharging pipe. According to an automatic ore dressing system and method through gravity, the maintenance is convenient, the operation is simple, and the comprehensive utilization rate of ore resources can be improved.