Environment-friendly anti-collapse drilling fluid and preparation method thereof

The invention relates to an environment-friendly anti-collapse drilling fluid and a preparation method thereof, and belongs to the field of petroleum drilling fluids. The environment-friendly anti-collapse drilling fluid comprises the following components in parts by weight: 100 parts of water; 2-6 parts by weight of sodium bentonite; 0.5-2 parts by weight of anti-collapse starch; 0.3-0.8 part byweight of high temperature resistant modified starch; 0.5 to 1 part by weight of polyanionic cellulose; 2-5 parts by weight of a humic acid fluid loss agent; 2-5 parts by weight of lignite resin; 0.2to 0.5 part by weight of sodium sulfite; 2-6 parts by weight of calcium carbonate with a particle size of 40-70 microns; and 5-10 parts by weight of calcium carbonate with a particle size of 10-30 microns. The environment-friendly anti-collapse drilling fluid is an environment-friendly anti-collapse drilling fluid system taking environment-friendly anti-collapse modified starch as a main agent; and the provided drilling fl