One of the major problems of commercial clean flame retardant materials is unstable mechanical properties because of high filler loadings. Clean flame retardant compositions having very low smoke and toxicity generation are invented by a method based on partial cross-linking of polymers. These composites are processed by routine thermoplastic extruder and do not use post curing system. Composition mainly contain 100 parts by weight (p/w) of resin (polyolefin or 100 p/w of polyolefin/ethylene propylene diene monomer rubber (EPDM rubber)), 90-150 p/w of non halogen content main flame retardants, 0.1-0.5 parts by weight of crosslinking agent, 1-20 p/w of auxiliary secondary flame retardant agents and 0.2-1.0 p/w of antioxidants. Clean flame retardant compositions use peroxide composite as a crosslinking agent and metal hydroxide composite as a flame retardant. The present invention demonstrates more reliable method for producing clean flame retardant insulations for wire and cable without deterioration of mechanical properties.