A versatile liquid dosing device along with its metering theory, which can be applied to both SCR dosing system and DPF regeneration system of IC engine after-treatment system, is presented in this paper. The device is composed of a solenoid driven plunger pump, a nozzle and a pressure tube, and is pump-end controlled by PWM signals. Both electrically resistive and conductive liquids including DEF for SCR system, fuel for DPF regeneration, and gasoline for spark ignition engine, can be dispensed quantitatively with this device.A metering theory determining the liquid discharged per injection is developed by studying the system using a physical-mathematical model. The study shows that the liquid discharge can be well correlated with a measurable variable T3, which is associated with the net output energy. Experimental investigations verified that the metering results were independent of the state changes. The developed device was able to work at a frequency from 0 to 80Hz with largest dosing range of 0 to14 L/h at 24 volt.The liquid dosing device was applied and tested on a SCR system as a verification example. The pump was so compact that it could be located at the bottom inside the DEF tank, which greatly simplified the anti-freeze design consideration and the SCR system. Tested results on a diesel engine with the SCR system showed good capability to reduce the engine NOx emission with high maximal NOx conversion rate and good controllability to achieve a NOx emission target with high reliability and high DEF efficiency.