Accordion-shaped traps are widely used in China to catch the Asian paddle crab C harybdis japonica but traps of conventional design often catch juvenile crabs. A new type of accordion-shaped trap with an escape vent(L×W=4.3 cm×3.0 cm) was designed and a comparative study between the newly designed and conventional traps was performed in the artifi cial reef area of Zhuwang, Laizhou Bay, China from June to August 2012. The mean catch per unit effort(CPUE) of undersized crabs was signifi cantly lower in the vented traps than in the conventional traps(paired t-test, n =30, P <0.001), while the CPUE of marketable crabs was signifi cantly higher in the vented traps(paired t-test, n =30, P <0.001). The mean size of crabs(carapace length) caught in the vented traps was signifi cantly larger than in conventional traps(paired t-test, n =29, P <0.001). The ratio of undersized crabs was 35.05%±2.57% in conventional traps and 12.53%±0.69% in vented traps(signifi cantly lower, paired t-test, n =29, P <0.001). Therefore, a 4.3 cm×3.0 cm escape vent was considered appropriate for C. japonica fi shing in the artifi cial reef area. This fi nding will assist the development of more sustainable and effi cient crab fi shing methods using accordion-shaped traps. Accordion-shaped traps are widely used in China to catch the Asian paddle crab C harybdis japonica but traps of conventional design often catch juvenile crabs. A new type of accordion-shaped trap with an escape vent (L × W = 4.3 cm × 3.0 cm ) was designed and a comparative study between the newly designed and conventional traps was performed in the artifi cial reef area of ​​Zhuwang, Laizhou Bay, China from June to August 2012. The mean catch per unit effort (CPUE) of undersized crabs was signifi cantly lower in the vented traps than in the conventional traps (paired t-test, n = 30, P <0.001) while the CPUE of marketable crabs was signifi cantly higher in the vented traps (paired t-test, n = 30, P <0.001). The mean size of crabs (carapace length) caught in the vented traps was signifi cantly larger than in conventional traps (paired t-test, n = 29, P <0.001). The ratio of undersized crabs was 35.05% ± 2.57% in conventional traps and 12.53% ± 0.69% in vented traps (signifi cantly lower, paired t-test, n = 29, P <0.001). Thus, a 4.3 cm × 3.0 cm escape vent was considered appropriate for C. japonica fi shing in the artifi cial reef area. This fi nding will assist the development of more sustainable and effi cient crab fi sh shing methods using accordion-shaped traps.