Based on the plasma discharge theory, three different forms of plasma igniters are designed, i.e. toroidal plasma igniter, disc and cylindrical plasma igniters. For different plasma igniters, the discharge characteristics of the igniters are investigated under the different forms of excitation power, voltage and gas pressure. The plasma igniters are compared with spark ignition. The results show that the plasma discharge stream can be produced by the plasma igniters. The discharge threshold voltage increases with the increasing air pressure. At low pressure, the discharge threshold voltage increases with the increasing pressure linearly, which is in accordance with the Paschen law. At high pressure, the discharge threshold voltage will deviate from the Paschen law.