In the ground simulation testing of aircraft systems, varieties of liquid flow meters and their corresponding flow meters are widely used in the hydraulic, flight control, power supply and other system tests. This paper analyzes the traditional methods of laboratory measurement of liquid flow meters in three aspects which are the flow meter connection, the liquid medium, and flow display mode. The result shows that optimization of the traditional methods of laboratory measurement is urgent. At same time, some liquid flow meters are too large and complicated to install and disassemble. This paper presents three novel methods for calibration of liquid flow meter online mode. These methods can avoid the disassembly and installation of the flow meter and improve the work efficiency, which have great practical value.