Based on the database monitored by the 1.26m National Astronomical Observatory-Guangzhou University Infrared/Optical Telescope, we studied the optical variabilities of FSRQ 3C454.3. The monitoring period was from 2016 October 17 to 2018 December 14, and there were 6701 observations covering the g, r, and i bands (2196 at the g band, 2214 at the r band, and 2291 at the i band). (1) The maximum variabilities were {Delta}m_g_=2.806+/-0.124mag at the g band; {Delta}m_r_=2.365+/-0.160mag at the r band; and {Delta}m_i_=3.126+/-0.070mag at the i band. (2) Among the gri intraday lightcurves, there are 172 portions of the data sets showing intraday variability (IDV). The distributions of IDV timescales ({Delta}T) can be profiled by a three-order Gaussian function, with the center values {Delta}T_1_=17.18min, {Delta}T_2_=34.91min, and {Delta}T_3_=68.92min. These results imply that the origin of IDVs is very complicated. (3) Based on the IDV timescales, we obtained the emission size R<=7.17x10^15^cm, fixed the broad-line region and modeled the spectral energy distributions. (4) We used the Jurkevich method, red-noise fitting, and the weighted wavelet Z-transform to analyze the long-term variabilities and obtained indications of a possible period of P=2.92+/-0.85yr, and used the binary black hole system to explain this period. Based on the long-term period, we can estimate the time until merger of the binary black hole, t_merge_=6.69x10^3^yr, and the luminosity of gravitational waves, L_G_=1.56x10^48^erg/s.