To provide a method for producing a polyolefin-based fiber highly oriented by a stretching method directly joined with a spinning simply at a low cost.

This method for producing a polyolefin-based fiber is to spin a polyolefin having ≥0.01 melt index(MI) from a spinneret 3 by melting it, pass the spun yarn through a heated towing zone 4 of which temperature is kept lower than the melting temperature (Tm) of the polyolefin directly below the spinneret and also within a temperature range (ΔT) in which the spun polymer does not essentially crystallize, introduce the spun yarn into heated zones 7, 8, 9 while keeping ≥Tm-ΔT temperature of it, stretch the spun yarn by ≥8 fold in the heated zones and wind the stretched yarn with a winding means 11.