There are more and more layers with low water injection rate in waterflooding oilfields such as daqing periphery, jilin, jidong and etc. The typical layered flowrate is usually 3-20m3/d. Layered low flowrate was still obtained by stepwise decline method no matter what downhole regulator is used. Test tolerance may reach 30% under this method for low flowrate test which result in poor accuracy. To improve low flowrate test accuracy, the method of collection flowrate test based on electromagnetic flowmeter was adopted. This paper designed a dowhnole instrument based on electromagnetic flowmeter which is used to test flowrate of waterflooding wells in oilfieds. Equipped with two active balls, the low fowrate test accuracy was enhanced through collection and increasing flow velocity which was effective to increase test accuracy for electromagnetic flowmeter. Then we did a group of laboratory tests. The results demonstrated the instrument based on electromagnetic flowmeter can keep the accuracy below 5% within the flowrate 3-20m3/d. Finally, an application case was introduced in jidong oilfieds with minimum flowrate 5.98m3/d. The application increased the accuracy and reduced the influence of interlayer interference. This technique can not only be suitable for the low permeability oilfield, but also for the conventional water injection wells.