Abstract: For the discretized solution of the multivariable strongly coupled differential equations in pressurized water reactor core thermal-hydraulic analysis, this study analyzes the block structure of the coefficient matrix. By considering the sparse distribution of different physical quantities, the coupling relationships among variables across different sub-channels, and the ordering of variables, the system is decoupled using a symmetric multiplicative field-split approach. By employing a symmetric multiplicative field-split approach, the system is decoupled. The extensive coupled equations are broken down into three subsystems based on physical fields for independent resolution. Additionally, a preconditioning strategy rooted in symmetric multiplicative field-split is developed. Numerical evaluations were performed under four representative operational scenarios with varying channel scales. In comparison to traditional preconditioning approaches that directly apply Algebraic Multigrid (AMG) or Incomplete LU (ILU) factorization to the entire algebraic system, the proposed method significantly enhances the convergence rate and solution precision of Krylov subspace iterations.