A loading way and a device with double levers and a changeable lever ratio is introduced. The device is composed of two levers,one main lever and one ministrant lever. According to the changeable lever ratio principle,force is applied by the main lever while the ministrant lever maintain the initial balance of the entire system. The changeable lever ratio principle indicates that the lever ratio alters via an individual weight moving alone the lever arm. The force applies to the specimen because of the lever ratio alternation. That is,the variational force is applied through controlling the position of the weight. The system restores balance after loading. With the loading method mentioned above,the operation of such device would be simple and the balance state is adjusted naturally at zero. The system force control is realized by precise displacement change,such method results to much wider force value and fewer errors. The frequency of weight move decides the speed of force application,therefore,this device enhances the loading efficiency. The basic principle of the machine is presented in details and the errors analyzed as well. Furthermore,an experiment to a 1 MN force standard machine which applies such techniques was conducted. Data and test result are also included . The force value accuracy class 0. 01 is achievable according to the test result.%提出了一种变臂比双杠杆原理的加载方法，该方法安放试件后无需配平，加载系统由主、辅两套杠杆系统组成，主杠杆利用变臂比原理施加载荷，而由辅助杠杆实现杠杆系统的初始平衡。将系统对力的大小和加载速度控制转变为位移的精密控制，可获得较宽的力值范围、较小的力值误差和高的加载工作效率。阐述了这种方法的基本原理，并做了误差分析。对所研制的1 MN 变臂比双杠杆式力标准机进行了检验，给出了试验数据和检验结果。力值准确度可以达到0.01％。
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