The invention discloses a temperature-resistant calcium-tolerant inverse emulsion polymer for drilling fluids. The polymer is prepared by polymerization of a sulfonic acid group-containing monomer water solution with a mass fraction of 50%, N, N-dimethylacrylamide, acrylamide, a crosslinking agent, water, white oil, a span-80 emulsifier, a propylene glycol monolaurate emulsifier, an OP-15 or Tween-80 emulsifier, an ammonium persulfate water solution or a potassium persulfate water solution with a mass fraction of 10% as an initiator, a sodium thiosulfate water solution with a mass fraction of 10%, an azodiisobutyl imidazoline hydrochloride solution with a mass fraction of 5%, soda ash, and an ethylenediaminetetraacetic acid disodium salt. The inverse emulsion polymer provided in the invention has good abilities of filtration loss reducing, viscosity increasing, flow pattern regulating, hydration dispersion inhibiting of clay and drill cuttings, and can improve filter cake quality, enhance drilling fluid lubricity, thus being suitable for various water-based drilling fluids and being able to be used as a high-temperature, high-salt and high-calcium drilling fluid additive.