One of the important measures proposed by the Chinese government to comprehensively implement the innovation-driven development strategy and promote the supply-side structural reform is to promote new industrialisation, and improving the development efficiency of new industrialisation in the Yangtze River Delta (YRD) city cluster is conducive to promoting economic restructuring and upgrading, enhancing regional competitiveness, and achieving sustainable development. Based on the panel data of 41 cities in the Yangtze River Delta Urban Agglomeration from 2005 to 2021,the super-efficiency SBM-ML model, Dagum's Gini coefficient, kernel density analysis, and the convergence model were applied to measure the development efficiency of new industrialisation and its dynamic evolution trend and convergence characteristics were analyzed. The results are as follows.The development efficiency of new industrialisation shows an overall growth trend, and the growth momentum mainly comes from changes in scale efficiency and changes in technological progress.The differences in the development efficiency of new industrialisation are generally shrinking, and the inter-regional differences are the main part of the efficiency differences.The spatial gap in the development efficiency of new industrialisation is gradually expanding, and there is a phenomenon of multilevel differentiation.The four large-scale cities are all There are σ-convergence and β-convergence, and the speed of convergence decreases in the order of type I cities, type II cities, mega cities, and the Yangtze River Delta urban agglomeration.