The invention relates to the field of high molecular materials, in particular to a halogen-free flame-retardant epoxy resin composition and application thereof. The composition comprises 100 parts ofepoxy resin, a halogen-free composite flame retardant provided with diphenylphosphine oxide flame-retardant groups, 5-15 parts of a main flame retardant, 0-10 parts of an auxiliary flame retardant, 2-30 parts of a curing agent and 0-1 part of a curing accelerating crosslinking agent. The composition further comprises a mixture of at least two of reinforced fibers, a flexibilizer, a filler, a silane coupling agent and a solvent. The composite flame retardant containing the diphenylphosphine oxide groups is high in flame-retarding efficiency and small in adding amount and has excellent compatibility and dispersity with the epoxy resin; and in the curing process, intermolecular dispersion with the epoxy resin can be realized, and the original transparent state of the epoxy resin is maintained. The finally cured flame-retardant resin composition has the advantages of low cost, high transparency, low water absorption rate, high glass conversion temperature, high thermal stability, low dielectric constant and dielectric loss, high flame retarding and the like.