On the basis of summarizing the calculating methods of minimum instreaming ecological flow at home and abroad, the improved wetted perimeter method is adopted to determine minimum instreaming ecological flow of upper reaches of Hangjiang River. According to its practical condition, Shiquan, Ankang and Baihe three hydrological station as the control cross sections are chosen. By means of comparison of the calculated results and the data obtained by Tennant method, the result shows that adopting the flexure wetted perimeter method is a reasonable choice, and that minimum ecological flows of Shiquan, Ankang and Baihe three hydrologic stations are 40 m3/s，70 m3/s，100 m3/s respectively，and the ratios represented by percentages of these discharges to long term average annual flows are 11.23%，11.08%，12.55% respectively.