The invention discloses a wear-resistant 450 steel austenite grain size detection method which comprises the following steps: 1) preparation of a sample; 2) quenching treatment: heating the sample to 800 DEG C-1000 DEG C, carrying out heat preservation for 20-60 minutes, and then quickly quenching the heated sample into water; 3) erosion: fully mixing a saturated picric acid solution and a washing liquid according to a volume ratio of 1:2-4 to obtain an erosion agent; and putting the to-be-tested sample after quenching treatment into the erosion agent, eroding for 3-6 minutes at the temperature of 20-50 DEG C, then taking out, washing cleanly with water, and blow-drying; and 4) grain grading: carrying out metallographic observation on the sample after blow-drying, taking pictures on austenite grains, contrasting with standard atlas by a comparative method, and grading. The saturated picric acid solution and the washing liquid are mixed to obtain the erosion agent, the erosion agent is adopted for eroding the high-strength wear-resistant steel 450, the purpose that only original austenite grain boundaries are clearly displayed and a matrix structure is not displayed is reached, and thus a condition is created for accurate evaluation of the original austenite grain boundaries.