The present invention relates to a heat treatment method for increasing the depth of hardening layer in a steel rail, and belongs to the field of steel rail production process. The technical problem to be solved in the present invention is to provide a heat treatment method for increasing the depth of hardening layer in a steel rail and a steel rail obtained with the method. The method comprises the following steps: cooling a finished rolling steel rail by natural cooling, till the temperature at the center of rail head surface is 660˜730° C.; cooling the steel rail by accelerated cooling at 1.5˜3.5° C./s cooling rate, till the temperature at the center of rail head surface is 500˜550° C.; increasing the cooling rate by 1.0˜2.0° C./s and further cooling down the steel rail, till the temperature at the center of rail head surface is 450° C. or lower; then, stopping the accelerated cooling, and cooling down the steel rail by air cooling to room temperature. With the heat treatment method disclosed in the present invention, a deep-hardening layer thicker than 25 mm can be obtained in the rail head part, the portion within 25 mm depth below the surface layer of rail head has hardness equivalent to the hardness of the surface layer of rail head, and the rail head is in a pearlite structure across its cross section. Thus, the service performance of the steel rail against the wearing incurred by the contact between the train wheels and the steel rails can be improved.