For realizing real-time 3D temperature field reconstruction of Ar plasma jet, an orthogonal area array CCD (charge coupled device) spectrum tomography experimental system was proposed according to spectrum relative intensity diagnosis method. The size of tested field was measured using comparison between the tested field image caught through CCD and the plotting paper image when plotting paper was placed in the tested field position with no plasma jet; the emission intensity distribution of tested field was obtained using stepping motor taking fiber probe to scan tested field, and the spectrum analysis instrument was used to show the spectrum intensity information. Based on spectrum selection principle of the spectrum relative intensity method, spectra at 696.5 and 763.5 nm were studied as characteristic spectrum. Novel grad attenuation was designed based on the size and intensity distribution of tested field for not exceeding limen of CCD and avoiding the spectrum information loss at tested field edge. The narrowband filter was set between grad attenuation and CCD, so the whole tested spectrum information can be stored in computer real-time. According to orthogonal two-view spectrum tomography reconstruction algorithm, when tested field is axially symmetric, the reconstruction result is well. So four area array CCDs is placed orthogonally, and the same spectrum narrowband filters are placed in front of two orthogonal CCDs to reconstruct 3D emissivity factor field. Based on the 3D emissivity factor field and spectrum relative intensity theory, 3D temperature field of the tested field was reconstructed satisfactorily. The reconstruction result showed that it agreed with the results from fiber scanning diagnosis system, and the uncertain degreed is 3.3%. The proposed experimental device meets the needs of real-time 3D temperature field reconstruction. It provided a stable base for real-time diagnosis of plasma jet density field, pressure field and velocity field.