Since carbon nanotube (CNT) was discovered, it has been focused due to its distinctive structure and performance. In electrochemical field, CNT can be used as the modified material to prepare CNT chemically modified electrode (CNT-CME) and shows excellent electrochemical performances. A CNT-CME was obtained via growing CNT on the graphite electrode in situ by catalyst chemical vapor deposition. The obtained grown in situ CNT-CME (named as GSCNT-CME) had shown good testing accuracy and good electrochemical response. In this paper, the GSCNT-CME was used to detect copper ion in water via the cyclic voltammetry. The results showed that the linear range of GSCNT-CME to copper was from 1.0×10-5 to 2.5×10–3 mol/L in 0.6 mol/L H2SO4 supporting solution (with the scanning rate of 10 mV/s). The linear range was exactly the most in need of detection Cu2+ concentration (from 1.57×10-5 to 1.0×10–3 mol/L) according to the Ⅱ, Ⅲ and Ⅳ drinking water national required standard (GB3838-83, ≤1.57×10-5 mol/L). And the detection limit was 2.64×10-6 mol/L (S/N=3). At the same time, the recovery of copper ion was 93.04%-99.79%. The results indicated that GSCNT-CME had the important value of practical application to rapid detect copper ion in water.