The invention relates to a molecular marker, primers, a kit and a detection method for rapidly detecting potassium content in flue-cured tobacco leaf. A segment for differential expression of desoxyribonucleic acid, which is about 2,000bp is obtained by an SSR-PCR technology; the segment is cloned by virtue of bacterial plasmids M13; and a base sequence of the segment is determined to be 2165bp by virtue of an automatic nucleic acid sequence analysis instrument. On the basis of the sequence, a pair of oligonucleotide primers is artificially synthesized; the oligonucleotide primers comprise probes which are capable of detecting the potassium content in the flue-cured tobacco leaf, namely detecting expression of potassium-related genes in the tobacco leaf, and can be used for detecting the potassium-related genes in tobacco leaf breeding. The method is simple to operate, reliable in result, and high in detection speed, and is not influenced by the growth and development periods of plants and the environment; and the identifying efficiency can be greatly improved.