The invention relates to a fiber product prepared by spinning of a copolymer spinning solution formed by polymerization of a diamine-containing meta-position monomer, a sulfonyl-containing monomer and an acyl chloride group-containing para-position monomer; also relates to a yarn, fabric and product containing the fiber, and a preparation method thereof. The fiber has good flame retardancy and mechanical properties, and can be widely used in the thermal resistant protection field.