  The photometric analysis and spectroscopic study of the long period low mass
ratio deep contact binary KN Per were executed. The light curves of
BV(RI)$_c$-band were from the Ningbo Bureau of Education and Xinjiang
Observatory Telescope (NEXT) at the Xingming Observatory. Through the analysis
of Wilson-Devinney (W-D) program, KN Per was found as an A-type low mass ratio
deep contact binary (q=0.236, f=53.4\%). A cool spot applied on the primary
component was introduced to explain the unequal maxima of the light curve.
Based on the O-C analysis, we found that the rate of the increasing orbital
period is $\dot{P}$ = 5.12 $\pm$ (0.30) $\times$ 10$^{-7}$ d/yr, meaning the
mass transfer from the secondary component to the primary one. By analyzing the
spectroscopic data, we detected chromospheric activity emission line
indicators, which is corresponding to the light-curve analysis. 71 long period
(P $>$ 0.5 days) contact binaries including our target were collected. The
evolutionary states of all collected stars were investigated by the
illustrations of mass-radius, mass-luminosity, and log M$_{T}$ - log J$_{o}$.
The relations of some physical parameters were also determined. With the
instability parameters of KN Per, we determined that it is a stable contact
binary system at present.
