Changes in sea level are global and cyclical; however, the understanding of the processes that control them is still very limited owing to the low rate of progress in technology to reconstruct the trajectory of global sea level change. Based on the reconstruction of the Cenozoic sea level change curve in the northern South China Sea, discrimination criteria for global sea level (GSL) and relative sea level (RSL) changes are proposed for the first time, and five technical difficulties in single-period trajectory reconstruction are addressed. The findings show that the recorded sea level changes are dominated by the GSL change component in only a small number of basins worldwide. The Cenozoic sea level showed an increasing trend of sea level, and the fluctuation amplitude of the second-order cycle was considerably smaller than that of the third-order cycle. These findings challenge the consensus that the Cenozoic sea level continues to fall and that the magnitude of the second-order cycle is greater than that of the third-order cycle. In terms of technological advancement, the accuracy of the third-order single-period trajectory was improved to approach the cosine locus by correcting the deviation between the sea level indicated by the residual accommodation space and the GSL, and eliminating the trajectory distortion caused by the differences in the deposition rate. The new technique has the potential to reconstruct original single-period trajectories, which can provide technical support for comparing the single-period sea level trajectory with the corresponding celestial orbit and studying the mechanisms driving primary cycles. •The global sea-level (GSL) curve since 33 Ma has been reconstructed.•A criterion for distinguishing GSL and RSL trajectories is proposed.•Five technical difficulties in single-period curve construction are addressed.•New findings challenges the consensus on GSL change.