Objective of this research was to investigate the effect of irrigation concentration on the growth and fruit quality of sweet pepper(Capsicum annuum L.) in fertigation. The sweet pepper was grown for 210 days with irrigation concentration of EC 0.5, 1.0, 1.5, 2.0, and 3.0 dSㆍ$m^{-1 }$ in fertigation nutrient solution developed by European Vegetable R & D Center, Belgium. The net $CO_2$ assimilation and transpiration rate were the highest in the treatment of 2.0 dSㆍ$m^{-1 }$. The pH in the soil was range of 5.63 ～6.03, the EC increased as the irrigation concentration was getting higher. The SPAD value also increased as the irrigation concentration was getting higher, N, P, K, Mg except Ca were highest in the treatment of EC 2.0 dSㆍ$m^{-1 }$. The growth was good in the treatment of EC 2.0 dSㆍm$m^{-1 }$. The fruit length, width, firmness, and pericarp thickness had no statistical differences among treatments, the fruit fresh weight and dry weight were good in the treatment of EC 2.0 dSㆍ$m^{-1 }$ the yield was good in the treatment of EC 1.5 dSㆍ$m^{-1 }$ and EC 2.0 dSㆍ$m^{-1 }$ The sugar contents was the highest in the treatment of EC 2.0 dSㆍ$m^{-1 }$ with 9.0$^{circ}$Brix. In conclusion, the optimal irrigation concentration for sweet pepper fertigation was EC 2.0 dSㆍm$^{-1}$ .