Text-Based Person Retrieval (TBPR) aims to identify a particular individual within an extensive image gallery using text as the query. The principal challenge inherent in the TBPR task revolves around how to map cross-modal information to a potential common space and learn a generic representation. Previous methods have primarily focused on aligning singular text-image pairs, disregarding the inherent polymorphism within both images and natural language expressions for the same individual. Moreover, these methods have also ignored the impact of semantic polymorphism-based intra-modal data distribution on cross-modal matching. Recent methods employ cross-modal implicit information reconstruction to enhance inter-modal connections. However, the process of information reconstruction remains ambiguous. To address these issues, we propose the Learning Semantic Polymorphic Mapping (LSPM) framework, facilitated by the prowess of pre-trained cross-modal models. Firstly, to learn cross-modal information representations with better robustness, we design the Inter-modal Information Aggregation (Inter-IA) module to achieve cross-modal polymorphic mapping, fortifying the foundation of our information representations. Secondly, to attain a more concentrated intra-modal information representation based on semantic polymorphism, we design Intra-modal Information Aggregation (Intra-IA) module to further constrain the embeddings. Thirdly, to further explore the potential of cross-modal interactions within the model, we design the implicit reasoning module, Masked Information Guided Reconstruction (MIGR), with constraint guidance to elevate overall performance. Extensive experiments on both CUHK-PEDES and ICFG-PEDES datasets show that we achieve state-of-the-art results on Rank-1, mAP and mINP compared to existing methods.