A kind of loading scale was introduced. The causes loading error were analyzed using data of field application. It was founded that the loading error is composed of measurement error and control error. It was concluded that the effective measures to improve loading precision are 1) setting work ways of A/D7730 reasonably, which considers the quantization error and measurement lag error can reduce the sum of the two errors to the minimum value; 2) using shock absorption measures; 3) reducing the radius of pushing spiral to the exit gradually to keep stability of the volume in the air; 4) supplying power to controlling device by using the isolated transformer to restrain the interference of high harmonics waves.