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 P ̇ = 5.12 ± (0.30) × 10−7 day yr−1, 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 –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.

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