For a methanol/diesel dual-fuel engine incorporating a waste heat recovery-coupled methanol gas-assisted injection system, waste heat recovery evaluation metrics were established according to energy flow analysis. These metrics assessed the impacts of gas-assisted pressure and methanol substitution ratio on methanol fuel utilization efficiency. The results indicate that methanol utilization efficiency increases with the rise of gas-assisted pressure at a constant gas-assisted temperature of 80 ℃ and methanol substitution ratio of 40%. Within the 0.1-0.2 MPa gas-assisted pressure range, the exhaust energy increase accompanied by the gas-assisted pressure increase leads to higher heat absorption efficiency of mixture and greater energy absorbed by methanol from the mixture. Consequently, the methanol fuel utilization rate rises from 50.19% to 95.26%. Under test conditions with a gas-assisted temperature of 80 ℃ and a gas-assisted pressure of 0.15 MPa, the methanol fuel utilization rate gradually decreases as the methanol substitution rate increases. The methanol fuel utilization rate is 97.23% when the methanol substitution rate is 10% and decreases to 62.95% when the methanol substitution rate is 50%.