We investigated the self-assembling structure in aqueous solution of polyelectrolyte poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), which has a rigid chemical structure of polyaramide in the main chain. It is found that PBDT exhibits a stretched semirigid conformation in solution, regardless of PBDT concentration, C-P, or salt addition. PBDT in water exhibits both a very low overlap concentration, C*, and a lower critical concentration of nernatic liquid crystal, C-LC*. In the intermediate region of C* < C-P < C-LC*, PBDT forms cluster-like isotropic self-assembly. Moreover, in the intermediate region of C* < C-P < C-LC*, the addition of NaCl induces the alternation of structure from a cluster-like isotropic self-assembly to a fiber-like anisotropic one. Further addition of NaCl induces a network-like huge self-assembling structure, as the stoichiometric molar ratio of [NaCl] to [NaSO3-] increases beyond 1. The semirigid polyelectrolyte probably has hidden potential for structural polymorphism in aqueous solutions in the presence of salt.