The invention relates to a method for treating kenaf straws enriched with heavy metals. By the method for treating the kenaf straws enriched with heavy metals, lightweight anti-cracking thermal-insulation mortar which contains the kenaf straws enriched with the heavy metals is prepared. The mortar comprises a cementing material, sand, kenaf straw fibers enriched with heavy metal ions, fly ash floating beads and kenaf straw cores enriched with heavy metal ions. By the treating method, the kenaf straws enriched with the heavy metals are safely and effectively utilized, the heavy metal ion leaching amount of the prepared thermal-insulation mortar is smaller than the content of the heavy metals in the kenaf straws by 0.1%, the kenaf straws enriched with the heavy metals are treated, secondarypollution to the environment is avoided, furthermore, the lightweight anti-cracking thermal-insulation mortar can be obtained, the anti-cracking property of the thermal-insulation mortar is enhanced,compared with mortar added with kenaf straws which are not enriched with heavy metals, the thermal-insulation mortar has the characteristics that the flexural property is increased by 5%-10%, the economic benefit and the social benefit are good, the market space and application prospect are wide, and the comprehensive benefit is quite remarkable.