The utility model discloses an improved ladder platform assembly structure and a ladder thereof, relating to a foldable laddered platform or footplate locking part assembly structure and a ladder thereof. The improved ladder platform assembly structure comprises a ladder platform; a locking hook is arranged on the ladder platform and used for locking the ladder steps, the locking hook is composed of an assembly part and a hooking part both of which are integrally molded, the locking hook has preset thickness which is used for the rib surface of the assembly part and the rib surface of the hooking part, the rib surface of the assembly part is a contact surface allied with the ladder platform; the assembly part is provided with a slide way hole for a pin roll to slide through; a spring assembly bolt is arranged on the rib surface of the hooking part and used for mounting a spring; one end of the spring is arranged on the spring assembly bolt and the other end is propped up by the side wall of the ladder platform; the hooking part is provided with an assembly groove for mounting the locking hook in, the assembly groove is provided with a pin roll hole for a pin roll to be fixed in, and a pin roll limiting key for limiting the sliding position of the locking hook is arranged next to the pin roll hole. In the utility model, the ladder has well-guaranteed stability and security and light weight.