Particle charging is an important process of particle removal in an electrostatic precipitator (ESP). A particle charge measurement system, which can adjust the flue gas temperature, was designed to study the effects of the flue gas parameters (i.e., temperature and humidity), main component of the particle, and discharge electrodes on particle charging. When the temperature changed from 300 K to 363 K, the particle charge increased with increasing temperature at the same applied electrical field strength. For the particles with a size of 0.73 µm, the average particle charge increased by 30% from 140 e to 183 e with increasing temperature from 300 K to 363 K. The particle charge was increased by 98% when the relative dielectric constant increased from 4.5 to 11.8 at −4.2 kV cm-1. The increase in relative humidity significantly affected the acceleration of particle charging. For particles with sizes greater than 0.1 µm, the average charge increased by more than 50% with increasing relative humidity from 30% to 80%. Discharge electrode optimization also enhanced particle charging. When the electrode was changed from the wire electrode (d = 1 mm) to the ribbon electrode, the particle charge was increased by more than 75% for 0.7 μm particles at −4.2 kV cm-1.