The laser absorption spectrum of the (5,0) and (6,0) bands of the A 2Πi←X 2Σ+ transition of CS+ has been recorded using velocity modulation spectroscopy enhanced by optical heterodyne and magnetic rotation effects. First, improved molecular constants for the ground state of the ion were determined by a global linear least-squares fit of combination differences from the (1,0) (5,0), and (6,0) bands. Then a standard model was used to analyze the perturbations between the vibrational levels of the A 2Πi state and high vibrational levels of the X 2Σ+ state, leading to molecular constants and perturbation parameters for the υA=5∼υX=13 and υA=6∼υX=14 complexes. A new set of equilibrium parameters has been derived for the A and X states by combining all the available spectroscopic data, weighted according to the accuracy of the input parameters. The equilibrium internuclear distances from the new analysis are X 2Σ+re=1.492 156(78) Å and A 2Π re=1.639 55(10) Å. The Rydberg–Klein–Rees potential energy curves for the A 2Πi and X 2Σ+ states were constructed using the improved equilibrium constants, and the Franck–Condon factors calculated for all vibrational bands up to υ″=11 and υ′=10 of the A 2Πi−X 2Σ+ system. The overlap integrals calculated from the RKR turning points were used to find the interaction parameters a and b from the experimental perturbation parameters ξ and η. The r dependence of the a and b values relevant to the perturbations in the (1,0), (5,0), and (6,0) bands is discussed.