Photometric analysis and spectroscopic study of the long-period low-mass-ratio deep-contact binary KN Per were performed. The light curves of the BV(RI)c band were from the Ningbo Bureau of Education and Xinjiang Observatory Telescope at the Xingming Observatory. Through the analysis of the Wilson-Devinney 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 dP/dt=5.12+/-(0.30)x10^-7^day/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 correspond to the light-curve analysis. Seventy-one long-period (P>0.5 day) 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_-logJ_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.