The invention discloses a method for producing high-hole-expansion-rate steel 420L for an automotive frame. The method includes the steel-making step and the hot rolling step; the steel-making step is characterized in that produced molten steel comprises, by weight, 0.06%-0.08% of C, 1.10%-1.20% of Mn, not larger than 0.008% of S, not larger than 0.020% of P, not larger than 0.10% of Si, 0.015%-0.035% of Als, not larger than 0.0050% of N and the balanced iron and inevitable impurities; and the hot rolling step includes the heating working procedure, the rolling working procedure and the cooling working procedure. The cooling working procedure includes the steps that strip steel enters a first set laminar cooling area at the temperature of 835+/-15 DEG C, and the strip steel is rapidly cooled at the speed ranging from 50 DEG C/s to 80 DEG C/s to the temperature of 690+/-20 DEG C; then air cooling within the temperature range is carried out for 2.3 s to 2.8 s; and finally the strip steel enters a second set laminar cooling area, and is cooled at the speed ranging from 20 DEG C/s to 40 DEG C/s to the coiling temperature of 460+/-20 DEG C. By means of the method, ingredient elements such as the C, the Mn and the Si are adopted, the steel 420L for the automotive frame in needed thickness and specification is produced through the subsection cooling process, and the metallographic structure of the 420L is shown in an attached map; and the development requirement for high-molding performance is met, a small alloy adding amount is added, and a huge economic benefit can be generated.