The invention provides a flame retardant material of a lithium battery module. The flame retardant material is disposed on the top surface and/or the side surface of the lithium battery module, and comprises the following components: in percent by weight, 0-50% of a triazine carbon-forming agent, 0-30% of aluminum diethylphosphinate, 0-30% of triphenylphosphine oxide, 0-70% of an epoxy resin adhesive and 0-70% of organic silica gel. The invention also provides a preparation method of the flame retardant material for the lithium battery module. Through the flame retardant material, combustion can be slowed down and stopped, ignition of the lithium battery module is avoided, and the safety performance of lithium ion batteries is improved greatly.