Abstract: With the ending in upsurge of pipeline construction in China, the new projects of the oil and gas pipeline companies will be reduced gradually. Therefore, higher requirements are put forward on the reasonable control of technical transformation investment scale in pipelines (hereinafter referred to as the technical transformation), the improvement of capital utilization efficiency, and the realization of safe and efficient pipeline operation. Herein, the Data Envelopment Analysis (DEA) model was established for the evaluation on the investment efficiency of the oil & gas pipeline companies. Meanwhile, the technical transformation investment efficiency of pipelines was evaluated from the three aspects of pipeline profit, energy consumption and cost based on the actual operation of PipeChina West Pipeline Company. In addition, the influence of scale and structure of technical transformation investment on its efficiency was analyzed and suggestions were proposed on the optimization of technical transformation investment. The results show that the efficiency of technical transformation investment is negatively related to the unit turnover investment and the proportion of technical transformation investment to depreciation and amortization. The higher the pipeline investment efficiency, the more sensitive the efficiency of technical transformation investment is to the change of those two investment scale indicators. For the pipelines with high investment efficiency, their technical transformation investment should focus on the new projects. For the pipelines with low investment efficiency, the technical transformation investment should focus on the renovation and safety risk control projects. Generally, the research results could provide theoretical reference for other oil & gas pipeline companies to prepare investment plans and optimize the scale and structure of technical transformation investment.