A period analysis of the data obtained in six nights of differential photoelectric photometry of the {delta} Scuti star DQ Cephei (about 42 hours) confirms the pulsation modes of f_1_=8.0480 cycle per day and f_2_=12.6826 cycle per day. The result adjusts well to the observations that cover a time span of 46 years. Comparing with the results obtained for different years, we discovered obvious amplitude variations of the two modes. These amplitude variations show phase differences of almost 180 degrees. The variation period probably is longer than 46 years.