This paper proposes a design of precision measurement of direct current. System USES STM32 type single-chip computer as the microprocessor control, the AD converter for access control and high precision to measure current sampling resistor voltage sampling, and the subsequent data processing, the front touch screen display and communicate with the computer. For sampling resistance after electrify resistance changes caused by heat causing inaccurate measurement problem, this paper developed by the institute of metrology "very low load effect distributed sampling resistor" current samples to be measured, to ensure the current sampling accuracy. Measuring parameter is set by the touch screen can also be by computer through the serial port to set the parameters of the measuring instrument, and realizes data acquisition and storage. This design scheme on a - 1A ~ 1A range of dc current measurement, by changing the different resistance of sampling resistor, can further expand the current measuring range. This article also design test scheme for high precision analog-to-digital conversion of these core modules and the whole system was tested, the measurement scheme has high measurement accuracy, good stability, the advantages of easy operation, can meet the needs of practical application.