A grating tuned long pulse ultraviolet (UV)-preionized TE CO2 laser excited by pulser/sustainer discharge is demonstrated. With gas mixture volume fraction of V(CO2):V(N2):V(He)=1:5:19 and total gas pressure of 30 kPa, the laser output pulse energies and laser pulse widths (full-width at half-maximum, FWHM) of altogether 75 spectral lines are obtained. The measured results show that with the same pumping parameters the laser pulse width of each spectral line differs considerably as the grating is tuned from one line to another. Detailed measurement is carefully made on the laser output pulse widths of the four spectral lines 9R(20), 9P(20), 10R(20) and 10P(20) under different discharge voltage, discharge pulse width or gas mixture volume fraction, which strongly illustrate that the laser pulse width in a tunable long pulse TE CO2 laser with pulser/sustainer discharge varies with the output laser wavelength. By simultaneously measuring the discharge current waveform and the output laser pulse profile, it is found that the variation of the laser pulse width at each spectral line is perhaps mainly due to the gain difference of each spectral line.