The helium (He) non-thermal atmospheric pressure plasma jet (APPJ) source was configured, and the He spectra were measured by applying AC power to the source. A He collisional-radiative (CR) model was developed to investigate the He spectra obtained from the APPJ source. Different atmospheric pressure (AP) processes were evaluated, and the dominant processes among them that contribute to the He spectra were determined. The plasma parameters of the APPJ were determined using the He CR model, and the He spectra were successfully reproduced. The electron density was determined to be ∼ 2 × 10 12 cm - 3 between the electrodes of the APPJ, and ∼ 9 × 10 11 cm - 3 outside the quartz tube, for a frequency and bias of an AC voltage source of 5 kHz and 10 kV p. p, respectively. A parametric study was performed to explain the behavior of the electron temperature and electron density of APPJ.