Optical Monitoring and Long-term Optical Spectral Variability of BL Lacertae Object S5 0716+714

We present photometric observations of the BL Lacertae object S5 0716+714 with a temporal resolution of 120 s in the Sloan i ' and r ' bands. These observations were conducted using the Comet Search Program telescope at Xingming Observatory from 2018 December 22 to 2020 February 15, and more than 5600 effective images were obtained on each filter across 79 nights. Additionally, we compiled long-term variability data spanning 34 yr in the optical UBVRI bands. Using the power-enhanced F-test and nested ANOVA test, we found intraday variability (IDV) on 31 nights and possible IDV on 20 nights in the i ' band. Similarly, IDV was detected on 35 nights in the r ' band, while possible IDV was observed on 22 nights. The minimum variability timescale is 7.33 +/- 0.74 minutes, and the estimated black hole masses are (0.68 similar to 5.12) x 108M circle dot. The spectral variability and long-term optical light curves reveal a bluer-when-brighter trend on intraday timescales. The long-term optical flux density and spectral index exhibit periodic variability with a timescale of about 1038 days. An anticorrelation between optical flux and spectral index was observed, with a time delay of -140 days. Variability across different optical bands exhibited a strong correlation, with no discernible time lag. From the IDV, spectral variability, correlation, and time delays between different bands, we conclude that these radiation characteristics may result from the shock-in-jet model scenario.