  Supermassive black hole binary (SMBHB) is expected with the hierarchical
galaxy formation model. Currently, physics processes dominating the evolution
of a SMBHB are unclear. An interesting question is whether we could
observationally determine the evolution of SMBHB and give constraints on the
physical processes. Jet precession have been observed in many AGNs and
generally attributed to disk precession. In this paper we calculate the time
variation of jet precession and conclude that jet precession is accelerated in
SMBHB systems but decelerated in others. The acceleration of jet precession
$dP_{\rm pr} / dt$ is related to jet precession timescale $P_{\rm pr}$ and
SMBHB evolution timescale $\tau_{\rm a}$, ${dP_{\rm pr} \over dt} \simeq -
\Lambda {P_{\rm pr} \over \tau_{\rm a}}$. Our calculations based on the models
for jet precession and SMBHB evolution show that $dP_{\rm pr} / dt$ can be as
high as about $- 1.0$ with a typical value -0.2 and can be easily detected. We
discussed the differential jet precession for NGC1275 observed in the
literature. If the observed rapid acceleration of jet precession is true, the
jet precession is due to the orbital motion of an unbound SMBHB with mass ratio
$q\approx 0.76$. When jets precessed from the ancient bubbles to the currently
active jets, the separation of SMBHB decrease from about $1.46 {\rm Kpc}$ to
$0.80 {\rm Kpc}$ with an averaged decreasing velocity $da/dt \simeq - 1.54
\times 10^6 {\rm cm/s}$ and evolution timescale $\tau_{\rm a} \approx 7.5\times
10^7 {\rm yr}$. However, if we assume a steady jet precession for many cycles,
the observations implies a hard SMBHB with mass ratio $q\approx 0.21$ and
separation $a\approx 0.29 {\rm pc}$.
