[ Background] Chain pin method possesses the advantages of simple setting, flexible,convenient in material selection and low cost, thus has been widely used in soil erosion monitoring,especially in production and construction project soil erosion monitoring. However, there are a lot of disadvantages in the practical application of it, such as the monitoring accuracy is not high, the results are affected by anthropogenic disturbances frequently, and it is vulnerable to destruction. Moreover, there are limitations of using it in soil erosion monitoring. In order to investigate the scope of applying chain pin approach in soil erosion monitoring, especially for production and construction projects, and to obtain the applicable conditions for soil erosion monitoring using chain pin method, authors focus on theoretically calculating the minimal threshold of soil erosion modulus according to the measurement accuracy and principle of the chain pins, which has practical significance in increasing measurement precision of soil erosion monitoring. [Methods] The study was conducted on a slope with 9 rods evenly distributed. First of all, according to the actual situation, we determined the measured minimal height of chain pins that the naked eye can observe, and we calculated the sample average minimal soil erosion thickness and erosion volume; then on the basis of the corresponding to different soil texture and soil bulk density, we calculated soil erosion per square km in the monitoring period, and converted it to annual soil erosion modulus. [Results] Among 9 measuring chain pins, we supposed that any single pin was measured with the height change of 1 mm, other 8 pins were 0 with naked eye for a certain period of monitoring time (such as monthly, quarterly, and annually), thus, the average soil erosion thickness of the whole monitoring plot was 1/9 = 0.11 mm, based on this thickness, we calculated the minimal erosion volume as 110 cubic meters per square kilometer. Then we obtained the soil erosion weight according to the volume of soil and soil bulk density. From the calculation results, the minimal threshold value of soil erosion modulus was 1 452, 484 and 121 t/ ( km²·a) for month, season and year,respectively. [Conclusions] It can be seen that the chain pin method can only be applied in the given region or period, where or when soil erosion modulus is above the calculated minimal threshold in this paper, or in the area with low soil erosion modulus. If chain pin method is applied in areas where does not meet the conditions mentioned above, there will be some limitations or even the monitoring data can't be acquired. It is suggested that other methods, such as sediment basin, should be adopted to ensure the accuracy of soil erosion monitoring results in areas or periods of lower soil erosion intensity than this min-threshold.