This paper studies the isotopic effect of Cl+2 rovibronic spectra in the A2∏u (Ω = 1/2) - X2∏g (Ω = 1/2) system.Based on the experimental results of the molecular constants of 35Cl+2, it calculates the vibrational isotope shifts of the (2, 7) and (3, 7) band between the isotopic species 35Cl+2, 35Cl37Cl+ and 37Cl+2, and estimates the rotational constants of both A2∏u and X2∏g states for the minor isotopic species 35Cl37Cl+ and 37Cl+2. The experimental results of the spectrum of 35Cl37Cl+ (3, 7) band proves the above mentioned theoretical calculation. The molecular constants and thus resultant rovibron/c spectrum for 37Cl+2 were predicted, which will be helpful for further experimental investigation.