The present invention discloses an siRNA that inhibits K-RAS gene expression, and the precursor sequences and applications thereof. The K-RAS siRNA and its precursor sequences provided by the present invention can efficiently inhibit the expression of the K-RAS gene, and in vivo experiments have shown that the K-RAS siRNA has a certain inhibitory effect on tumours highly expressing K-RAS. The precursor of the siRNA of the invention and its vector can form a stable siRNA that functions in a host.
