Both inflation and economic growth have important effects on social welfare. By expanding Lucas' (1987) welfare cost calculation model of economic growth decline, and introducing inflation into the model, the impact of inflation on welfare cost of economic growth slowdown was discussed. Inflation has an impact on welfare costs by affecting the discounting behavior of representative consumers. The welfare costs of slower growth have fallen as inflation has risen; Under the new normal, the welfare cost caused by economic growth slowdown is 5.38%.