We systematically search for quasi-periodic oscillatory (QPO) signals on the
monthly time scale among the 1525 sources given in the Fermi Large Area
Telescope Light Curve Repository (LCR). We find a transient QPO of 31.3$\pm $ 1.8
days in the gamma-ray band light curve of the TeV blazar S5 0716+714, which has
7 cycles (MJD 55918-56137) for the first time by Weighted wavelet Z-transform
(WWZ) and Lomb-Scargle periodogram (LSP) methods. Monte Carlo simulations based
on power spectral density (PSD) and probability distribution function (PDF)
were used to evaluate the confidence level of the QPO, and the result is $\sim 4.1\sigma $ . Seasonal Autoregressive Integrated Moving Average (SARIMA)
modeling of the light curve revealed it is a significant physical QPO. the
physical models to explain the sporadic QPO of the month time scale in blazar
were discussed. Our studies indicate that the helical jet model and blob move
helically in a curved jet model to properly explain this kind of transient QPO.