By analyzing the judicial appraisal case of Xianyou Stone Art Culture City, which involves dual pricing methods, incomplete performance status, and defective change order documentation, this study proposes a logical framework for issuing selective appraisal opinions when contract pricing clauses conflict. Based on the authenticity, legality, and relevance of change order documents, these are categorized into three levels of validity: definitive, inferential, and non-allowable. A "reverse deduction from budget price" method is adopted to reconstruct the calculation algorithm for deducting unfinished work costs under fixed-price contracts. Building upon this foundation, a standardized approach is developed for the entire process of construction cost judicial appraisal, encompassing prevention at the front end, control during execution, and coordination at the back end, aiming to provide practical, technically feasible, and legally acceptable guidance for complex construction cost appraisals.