The invention relates to a preparing method for an ordinary-pressure positive-
ion dyeable 
polyester fiber. The preparing method includes the steps that dimethyl isophthalate-5-
sodium benzenesulfonate,
ethylene glycol, a catalyst and an anti-
ether agent are mixed to be subjected to an ester exchange reaction, the reaction is end, then 
ethylene glycol and 
sodium ethylene glycol are added, modulationis carried out, then 
terephthalic acid, 
ethylene glycol and a catalyst are mixed, and the mixture is subjected to an 
esterification reaction; the modulated product after the ester exchange reaction is end and 
polyethylene glycol are added into an 
esterification reaction system reaching the end point of the 
esterification reaction, condensation 
polymerization is carried out, and 
spinning melt is obtained; the 
spinning melt is measured, extruded, cooled, subjected to oil applying, stretched, subjected to 
heat setting and wound, and the ordinary-pressure positive-
ion dyeable 
polyester fiber is prepared. According to preparing method, generation of impurities in the 
polyester-
fiber production process is reduced, pressure rising of a 
spinning assembly and a filter is reduced accordingly, the service cycle of the polyester fiber is prolonged, the continuity and the safety of the whole production process are guaranteed, and the preparing method has the good economic value and popularizationvalue.