Inspired by the human expert thinking paradigm in operations research, this work introduces a new concept of reasoning tasks: Textual Constrained Optimization (TCO) problems. A TCO problem is characterized by a natural language description that implicitly specifies an underlying structured model with variables, constraints, and objectives. We propose a novel Syllogism-driven Textual Constrained Optimization Reasoning (STCOR) paradigm, driven by classical syllogistic logic. Unlike contemporary stepwise methods, our framework structures reasoning into three phases: meta-modeling, which acts as the major premise by retrieving a relevant class-driven prototype template; formalization, which serves as the minor premise by instantiating the template into an explicit logical model from textual queries; and solving, which derives the final answer as conclusion. To support the end-to-end implementation, we further develop a tri-level optimization algorithm TriRL.