The new results of the evolution of the synchrotron peak for Mrk 421 are mo
stly likely related to the particle acceleration process. In order to accou
nt for the above results, we present a model of blazar variability during t
he flare in which the emission comes from accelerating electrons. A diffusi
on advection equation of the electron energy distribution is derived to cal
culate the spectrum and light curve of synchrotron radiation. We present th
at the observed shifts of the synchrotron peak moving to higher energies du
ring the flare are caused by shock acceleration. The observed relation betw
een changes in the fluxes at specified frequency ranges and shifts of the p
eak position is fitted to constrain the physical parameters of the dissipat
ion region.