By using vacuum in-line driving and photoluminescence measuring system, we have examined the electrical and optical characteristics of plasma display panel produced by vacuum in-line sealing technology. In addition, the relationship between luminous efficiency and base vacuum level before filling discharge gas was analyzed. In the case of base vacuum level of $1.33{ imes}10^{-1}$ Pa, the firing voltage of a 2-inch diagonal PDP panel was ranged from 312 to 343 V depending on the discharge gas pressure of $2.667{ imes}10^4$ to $4{ imes}10^4$ Pa at room temperature, Whereas in the case of $1.33{ imes}10^{-4}$ Pa, the firing voltage was reduced by 40 V and luminescence was improved slightly.