Abstract: Aiming at present deficiency in getting the external load of loader oil cylinder，the determination method of the external load change characteristic of loader bucket cylinder is investigated.Based on establishing the external load mathematic model of bucket cylinder，the hydraulic pressure and piston displacement of bucket cylinder were actually tested and processed when loader shovels loose soil，and the change courses of the hydraulic pressure of rodless chamber，rod chamber and piston displacement of single typical operating cycle were obtained.In the paper，matlab was applied to fit the hydraulic pressure and piston displacement at different operating segments of the obtained single typical operating cycle，and by the programming process，the external load waveforms of different operating segments of bucket cylinder were obtained.After the waveform of each work segment was merged with nsoft software，the external load change characteristic curve of bucket cylinder when loader shovels loose soil was acquired.The analysis result showed that the determined external load change characteristic of bucket cylinder was consistent with the actual working condition.

Key words: Loader, Bucket cylinder, External load, Mathematic model, Change characteristic, Determination method