Abstract: Climate smart agriculture (CSA) can realize the pareto optimality in the three dimensions of “productivity & income - climate adaptation - emission mitigation”, particularly for the rural livelihoods and national food security. The development level of CSA can be evaluated in sustainable agricultural practices. In this study, an assessment framework was constructed for the development level of CSA from the three dimensions, according to the complex system collaboration. The development levels of CSA were quantitatively evaluated in each dimension, such as the climate smart index (CSI), in the major grain-producing areas from 2013 to 2022. There were trade-off relationships among multiple objectives in each dimension. The results show that: 1) The CSI of the major grain producing areas increased from 0.052 to 0.403 from 2013 to 2022, which was at a lower level but with an upward trend. The scores in the three dimensions of the CSA increased from 0.150, 0.119, and 0.110 to 0.624, 0.589, and 0.568, respectively. There were fluctuating characteristics in line with the trend of the CSI. The score of Productivity & Income was generally higher than that of Climate Adaptation and Emission Mitigation. It infers that the major grain producing areas were in the initial stage of CSA development. 2) The development level of CSA in the major grain producing areas shared a significant spatial non-equilibrium, with the spatial pattern shifting from dispersal to agglomeration. The regional gap was gradually narrowing. The contiguous climate-smart areas were observed in the major grain producing areas in North, Northeast, and Central China. There was a consistent trend of the three dimensions in the majority of the provinces, with the level of development increasing each year. 3) The correlation between multiple objectives under the three dimensions of CSA was dominated by synergy, where one dimension often benefited the rest. The degree of synergy in the multiple objectives was dominated by balancing the development of the three dimensions and the overall development level of CSA. Among them, “agricultural economic resilience ecological carbon sink” shared the strongest synergy, while the objective of “food production capacity - ecological carbon sink” shared a significant trade-off. There was a regional correlation between the other objectives. Region-specific technologies were adopted to accelerate the CSA for the differentiated policy interventions using regional disparities. Synergistic objective management was optimized to integrate the agroecology with precision farming. The assessment framework was proposed for the CSA development in sustainable agriculture. The key synergies and trade-offs were identified to mitigate the multidimensional conflicts in the CSA implementation, green transformation, and food security under climate change. The finding can also serve as a strong reference for the developing economies.