Abstract: Feldspar dissolution is the main controlling factor of secondary pores in Chang-8 reservoir of District DZ-ZY, Xifeng oilfield. This study uses the thin section, scanning electron microscopy(SEM), electron microprobe (EMPA) and other analytical techniques to analyze the characteristics of feldspar dissolution. Meanwhile, based on the properties of incongruent dissolution and theoretical calculations of secondary porosity and dissolution rate of feldspar, 4 kinds of feldspar dissolution intensity are determined: weak dissolution (dissolution rate <25%), medium dissolution (dissolution rate of 25%~50%), strong dissolution (dissolution rate of 50%~75%) and extremely strong dissolution (dissolution rate >75%). Feldspar dissolution commonly occurs in the study area and the contribution of feldspar dissolution pores to reservoir spaces reaches 60%. But there are significant differences among the dissolution degrees of different feldspar. The degree of dissolution of potassium feldspar is higher than that of plagioclase, and the dissolution pores of potassium feldspar accounts for the largest proportion. The dissolution of feldspar in the study area is dominated by medium dissolution (about 40%) and strong dissolution (about 36%). The contribution rate of potassium feldspar dissolution increases along with the dissolution rate and that of plagioclase is the opposite especially under the conditions of relatively high dissolution intensity