To explore whether strontium otolith-marking technology can be applied to evaluate the effect of grass carp stocking in aquaculture, 9-d-old larval grass carp (Ctenopharyngodon idellus) were used. They were immersed for 2 d in 80 mg/L strontium chloride hexahydrate (SrCl₂•6H₂O). After the immersion, the fish were sampled continuously during the rearing process, and the pre-treated otoliths examined by electron probe micro-analyzer. We used mapping and line analysis to investigate the elemental fingerprinting effect of strontium on the otoliths of grass carp larvae and captured the exact time of formation on the first day and the time lag of strontium marking based on counting of the daily rings of the three otolith types in grass carp. The results of the quantitative line analysis showed that immersion with 80 mg/L SrCl₂•6H₂O solution for 2 d caused strontium-marking peaks to form on the grass carp otoliths. The strontium-marking peaks of lapillus and sagitta were higher than those of asteriscus and gradually decreased to normal levels with an increase in recovery feeding time. Both lapillus and sagitta also had greater Sr and Sr/Ca ratios than asteriscus during the phase when the three otolith types did not show an increase in Sr values or Sr/Ca ratios. The mapping analysis results were consistent with the line analysis, and the marked areas in the three otolith types showed obvious red patterns, while the unlabeled low-strontium otolith areas showed blue patterns. In addition, through the comparative analysis of strontium-marking characteristics and the number of otolith growth days, it was found that among the three otolith types, the formation time of asteriscus was later than that of lapillus and sagitta, with the first daily increment formed at the 12th day of hatching, while lapillus and sagitta formed the first daily increment at the 2nd day of hatching. There was a 1-d time lag between the beginning of strontium-marker formation and the start of immersion and the disappearance of strontium markers and the end of immersion for lapillus and sagitta, respectively. Strontium markers were observed to appear in the core of the asteriscus, and the disappearance of the strontium-marker signals was observed with a time lag of 1 d from the end of immersion. Here, in terms of fish mortality and behavior, the Sr dose had no significant difference (P＞0.05) between the control and experimental groups. Considering the effects of marking due to the absorption of strontium by different otoliths and the differences in the morphology and structure of otoliths, as well as the difficulty of sampling, it is recommended that lapillus be used as the most suitable otolith for the observation of Sr markings of grass carp larvae. This can provide a theoretical basis and technological support for marking and detection of the stocking of grass carp and other cyprinids.