The invention discloses a method, a device and a system for radioactive source positioning. The method comprises the steps of acquiring a relation between a crystal count ratio in a crystal array of a detector and the radioactive source angle according to analog data; measuring the actual crystal count of the crystal array when the radioactive source under test radiates rays; acquiring a plurality of denoising crystal count ratios according to the actual crystal count and the various count noises within a variation range of count noises, acquiring actual radioactive source angles corresponding to the denoising crystal count ratios according to the relation between the crystal count ratio and the radioactive source angle, and selecting the actual radioactive source angle when the count noises are optimum as the radioactive source angle of the radioactive source under test. The device comprises a processing module, a measuring module and a calculating module. The system comprises a radioactive source positioning device, the radioactive source under test and the detector. According to the invention, the crystal count ration is adopted to act as a calculation parameter, effectively noise deducting technologies are adopted, and the sensitivity and the accuracy of radioactive source positioning are improved.