This packing weigher is a high-tech product which integrates mechanical and electrical technologies and suitable to the auto quantity-fixed working procedure on the packing production line. The controlling process of the balance is that: during work, under the control of the instrument, the material-discharging door is closed first and the balance is automatically reset excluding the unit case. In case the material is added by switching on feeding unit, when it enters into measuring hopper, the force sensor will transform its weight into corresponding electrical signal and send it to the instrument for data processing, the corresponding material weight will be displayed on the panel window, and all section’s controlling signals are outputted in turns according to the set parameters to let the feeding unit continuously add the material into the hopper with fast, minimum and slow three different speeds to complete the accurate and quantity-fixed material adding. After the material is completely added, the material-adding unit closes, and the material-discharging door beneath the measuring hopper opens, the material, relaying on its self-weight, pours into the bag through bag-catching tank. After the material is discharged, the material-discharging door closes and the bag-catching unit automatically opens to free the bag, thus one working cycle is finished and the controlling instrument automatically comes to the next working cycle. The approach switch beside the bag-catching tank is used to control the close of the bag-catching brace. Only when the bag-catching unit is under catching status, the instrument can give bag-pouring controlling signal.