As a kind of temperature sensor, the platinum resistance has a wide application in many industrial sectors and fields of aerospace due to its advantage of high accuracy, long-term stability, repeatability and interchangeability. In this paper, a method of nonlinearity correction of platinum resistance is presented based on a voltage-controlled current source. The method is featured in easy circuit design and parameter calculation. It was applied to an onboard radiometric calibration system, and both the corresponding circuit design and laboratory data were presented. It is shown that, the measuring error caused by the nonlinearity is reduced to 0.016℃, within a measuring range of -40~70℃.