Since Conway first outlined fundamental principles of micro-diffusion technique in 1957, it was then adapted to prepare samples for ¹⁵N isotope measurements. Currently it has been widely developed for nitrogen isotope measurements on ammonium (NH₄⁺) and nitrate (NO₃^–) in solid and aqueous samples. Compared with traditional distillation method, micro-diffusion technique is advocated because it eliminates cross contamination and requires less operator skill and time. However, the accuracy and sensitivity of this technique is still limited by some factors, including N recovery, isotopic fractionation and blank size. Another main limitation of micro-diffusion is that the results can’t be obtained immediately because diffusion is typically performed for at least one to several days. Thus, how to improve the sensitivity and accuracy of this technique and accelerate the diffusion process have become key research focuses. In this paper, aiming to promote using micro-diffusion technique in research of soil nitrogen transformation, the primary principles and factors impacting this technique were briefly summarized and introduced.