The invention relates to a method for detecting and evaluating continuously cast steel billet primary cooling effects. The method includes 1, taking samples; 2, preparing and treating test specimens, to be more specific, accurately 
grinding and 
machining detection surfaces of test specimen blocks, corroding the detection surfaces of the test specimen blocks in 
nitric acid solution and absolute ethyl 
alcohol corrosive agents with the concentration equal to or higher than 96% for approximately 30-120 seconds, taking the detection surfaces of the test specimens out of the 
nitric acid solution and absolute ethyl 
alcohol corrosive agents, washing the detection surfaces of the test specimens by the aid of 
distilled water, cleaning the detection surfaces of the test specimens by the aid of absolute ethyl 
alcohol and then 
drying the detection surfaces of the test specimens; 3, imaging the test specimens, to be more specific, observing the detection surfaces of the treated test specimens by the aid of a research-grade 
stereo microscope under appropriate multiple conditions and measuring and photographing typical positions; 4, evaluating the primary cooling effects, to be more specific, observing and computing the thicknesses of chilled 
fine grain layers of cast billets and the sizes and the morphology of each single crystalline grain according to obtained images, analyzing the appropriateness and the uniformity of the thicknesses of the chilled 
fine grain layers and evaluating the primary cooling effects. The method has the advantages that the clear images of solidification structures of samples can be quickly and visually obtained, the thicknesses of the chilled 
fine grain layers of the cast billets can be further measured and analyzed according to the images, and accordingly the 
continuous casting primary cooling effects can be reliably and comprehensively analyzed and evaluated.