For homogeneous isotropic turbulence study,the acquisition of band-pass filtered velocity increments(FVI) in a non-forced turbulent box is still a challenge both experimentally and numerically.Turbulence and associated physical processes,at a given instant,are permanently contaminated by a forcing process which can seldom be universal.The situation tends to be the origin of intermittency and the non-Gaussian probability density distribution for acceleration and velocity gradients.To reveal implied mechanism,grid turbulence is adapted to observe non-perturbed homogeneous isotropic turbulence.The velocity increments(VI) can be obtained following Comte-Bellot and Corrsin(GCBC) by means of two point-two time shifted velocity measurements.It is difficult to obtain decaying turbulence(DT) at large turbulent Reynolds number without pollution coming from walls.Nevertheless it is also significant to investigate DT in low Reynolds number regimes to determine non-polluted tendencies.The similarity of DT between particle image velocimetry(PIV) and hot wire anemometry measurements by GCBC are presented.Here we focus our tendency on VI and FVI probability density function(PDF) shapes in this letter.In conclusion,the tendency to Gaussian shape in inertial zone wavenumbers,demonstrates that there will be no intermittency if turbulent cascade is not perturbed. For homogeneous isotropic turbulence study, the acquisition of band-pass filtered velocity increments (FVI) in a non-forced turbulent box is still a challenge both experimentally and numerically.Turbulence and associated physical processes, at a given instant, are ****** contaminated by a forcing process which can seldom be universal. The situation tends to be the origin of intermittency and the non-Gaussian probability density distribution for acceleration and velocity gradients. To reveal implied mechanism, grid turbulence is adapted to observe non-perturbed homogeneous isotropic turbulence. velocity increments (VI) can be obtained following the Comte-Bellot and Corrsin (GCBC) by means of two point-two time shifted velocity measurements. It is difficult to obtain decaying turbulence (DT) at large turbulent Reynolds number without pollution coming from walls. Nevertheless it is also significant to investigate DT in low Reynolds number regimes to determine non-polluted tendencies. Similarit y of DT between particle image velocimetry (PIV) and hot wire anemometry measurements by GCBC are presented. Here we focus our tendency on VI and FVI probability density function (PDF) shapes in this letter.In conclusion, the tendency to Gaussian shape in inertial zone wavenumbers, demonstrates that there will be no intermittency if turbulent cascade is not perturbed.