Three modes of discharges, including diffuse, streamer, and patterned discharges , are achieved in dielectric barrier discharge in argon at 40 kPa gas pressure b y using a dielectric barrier discharge device with water electrodes. The electri cal and optical characteristics of the discharges are investigated. The voltage drop across discharge gap is obtained by measuring the voltage drop across the t est capacitor. Results show that the moment of discharge initiation is shifted e arlier and duty ratio of the discharge increases as the applied voltage increase s. At the moment of discharge initiation, the voltage drop across the discharge gap decreases and the transported charges abruptly increase. So the waveforms of the voltage drop across the discharge gap and the transported charges deviate from sinusoidal. The relationship between the voltage drops across the discharg e gap and the transported charges is nonlinear. Also the relationship between th e voltage drops across the discharge gap corresponding to zero applied voltage a nd the applied voltage is given. The function of wall charges and the influence of them on the voltage drops across the discharge gap and the transported charge s are discussed.