This research assessed the effect of five tagging methods: namely, PIT marking, fin amputation marking, fluorescent marking, ultrasound marking and T-type marking, on the critical swimming speed of grass carp . Grass carp with a body length of 15-25 cm (standard length, SL) were divided into three size groups: short body length (15-18 cm), medium body length (18-21 cm) and long body length (21-25 cm). Critical swimming speed was measured for 144 fish in an annular flume with a water temperature of (16±1)℃. SPSS17.0 software was used for data processing. The results showed that the absolute critical swimming speed of the grass carp tended to increase, while the relative critical swimming speed tended to decrease along with an increasing body length. Ultrasonic tagging showed a significant impact (<0.01) on the swimming ability of the fish in all size groups (body length 15-25 cm). The absolute critical swimming speed of the grass carp in each of the three size groups (short, medium, large) decreased by 18.72%, 16.40% and 23.15%, respectively, after ultrasound tagging, and the relative critical swimming speed of the three groups decreased by 18.95%, 17.78% and 21.86%, respectively. T-type tagging also showed a significant impact (<0.01) on the swimming ability of grass carp in the short body length group: their absolute critical swimming speed decreased by 8.35%, whereas their relative critical swimming speed decreased by 9.30%. No significant impact of T-type tagging was detected on the critical swimming speed of grass carp with a medium or long body length (18-25 cm). Finally, no significant impact on swimming speed was detected for fish with a PIT tag, fin amputation marking or fluorescent tag.