Inbreeding depression has long been observed because it exists in ourselves due to consanguineous mating. Inbreeding may reduce population fitness through the expression of recessive, deleterious alleles in homozygous form. Inbreeding depression is influenced by lineage effects, mating system, environment stress and so on. Human disturbance and overexploitation are the main reasons causing population decline and consequently inbreeding depression. For species conservation and restoration, we should take inbreeding into consideration.