The detrital section method for measuring structural state of potash feldspar on the un iversal stage is developed on the basis of thickening the thin section and selecting the section perpendicular to a-axis and also according to the fact that this mineral has well-developed(100)，(110) and (201) planes. The stability and repeatability of the measurements are quite good. Potash feldspar detrituses in the size of 0.2-0.3mm are chosen as samples to be measureds from them the detrital section fit for universal stage is made up,For the potash feldspar crystals approximately perpendicular to a-axis section, conoscopy or four axis method is used to measure the included angle of 2Y and Ng∧⊥(010) or Ng∧⊥(001) and calculate the optical ordering and triclinity. Practice shows that，as the measurement with detrital section method is simple to operate and has reliable precision, it d.eserves widespread utilization.