The invention belongs to the technical field of molecular biology and genetic engineering and in particular relates to siRNA and application thereof. SiRNA has double strands and is capable of inhibiting expressions of chicken BCL11B genes, and the sequence of siRNA refers to a positive-sense strand 5'GGGACAGUCAAUGGAAGAA3' and an antisense strand 5'UUCUUCCAUUGACUGUCCC3'. When the chicken BCL11B genes are interfered by siRNA provided by the invention, the interference efficiency on a transcriptional level can reach 91%, and siRNA is extremely high in interference efficiency, high in specificity, high in sensitivity, simple and convenient in operation, short in experimental period and low in price. SiRNA disclosed by the invention provides a direct and effective experimental tool for researching action mechanisms of the BCL11B genes in Marek's disease and other poultry diseases. SiRNA disclosed by the invention can be used for preparing medicines for preventing or treating chicken T-cell malignant lymphoma and preparing medicines for treating chicken Marek's disease.