The main factors affecting the accuracy of Wheatstone bridge are the sensitivity of Wheatstone bridge and the error of resistance box.In order to simplify the problem and obtain semi qualitative, semi quantitative and approximate theoretical results,an approximate model of resistance error is established. Combined with the existing theoretical formula of bridge sensitivity, the theoretical values of bridge arm resistance Rand R, when the measurement accuracy is the largest (extreme) are derived by calculating the error minimum.In addition,some practical problems are analyzed and discussed in detail.Although the results obtained are approximate. the research ideas. methods and concusions may not only provide theoretica guidance for Wheatstone bridge experiment,but also provide some clues and references for relevant theoretical research.