The invention provides a semi-chromatography gamma scanning method for low-medium radioactive waste barrel measurement. A rotary platform, a detector platform, a detector with a collimator, a transmission source platform, a transmission source, a shielding part of the transmission source and an analysis module are adopted in the method. A waste barrel is divided into multiple section layers in the height direction, the waste barrel is rotated, surface distribution of radioactive point sources on the section layers is changed into linear distribution of ring sources in the radius direction, the detector conducts measurement at different section layer heights and different eccentric positions in the section layers, an equation set reflecting the mutual relation between the detector counting rate and the activity of nuclide in annular grids is established, the equation set is solved, distribution of the activity of the radioactive nuclide in the waste barrel in the diameter direction and the height direction of the barrel is acquired, and the total activity of the radioactive nuclide in the waste barrel is acquired through summation. The method is high in measurement accuracy, short in measurement time and high in practical value and application prospect.