The invention discloses a rope ladder for metal roof board mounting and a metal roof board mounting method. The rope ladder comprises a rope ladder structure, fixed supports and purline connecting plates, and the purline connecting plates are fixedly connected with purlines through fixed bolts. The method comprises the steps that a, the purlines are mounted; b, the rope ladder structure is connected with buckles; c, the rope ladder structure is coiled; d, the rope ladder structure is mounted on the purlines; e, a rope ladder unfolding device is mounted; f, the rope ladder structure is unfolded; h, a metal roof board is mounted; i, and the rope ladder structure is dismounted. According to the rope ladder for metal roof board mounting and the metal roof board mounting method, the operation of directly mounting the rope ladder on purlines at the top of a house structure is canceled, the rope ladder structure is fixed on the fixed supports, the fixed supports are supports of rigid structures and are used as bearing components of the rope ladder structure, the gravity of the rope ladder structure and constructors is uniformly dispersed on the purlines, connection is reliable, and safetyis high.