Abstract: A kind of hydrophobic flame-retardant fiber and a preparation method thereof are provided by the present invention. The fiber has a skin-core structure, wherein, the volume ratio of skin to core is in a range of 2:8-6:4; weight percentages of compositions of skin layer material include: 79.9%-88.8% of PET (polyethylene terephthalate), 8%-13% of PVDF (polyvinylidene fluoride), 3%-6% of flame-retardant agent, 0.1%-0.5% of compatibilizer, 0.1%-0.6% of coupling agent; weight percentages of compositions of core layer material include: 91%-95% of PET, 5%-9% of flame-retardant agent.