The invention relates to a low-cost mineral processing technology for high-silicon high-calcium magnesite. The low-cost mineral processing technology comprises the steps of raw material crushing operation, grinding operation and flotation operation. The low-cost mineral processing technology is characterized by comprising the following specific technological steps that raw magnesite is crushed through a medium crusher, grinding operation is conducted through a closed circuit grinding assembly composed of a primary grate ball mill, a secondary grate ball mill and a spiral grading machine, an overflow product with the particle size of 70-80% of the overflow product being -0.076 mm is obtained and subjected to flotation operation adopting primary reverse flotation and primary obverse floatation, the magnesite comprising 46.50-47.00% of magnesium oxide, 0.80-1.50% of silicon dioxide and 0.90-2.00% of calcium oxide is obtained, wherein the concentrate yield is 82.00-90.00%, and the recovery rate is 81.45-85.00%. The low-cost mineral processing technology has the advantages that flotation operation adopting only primary reverse flotation and primary obverse floatation, thus, the grade of the silicon dioxide in the high-silicon high-calcium magnesite can be lowered to 0.5-1.5% from 2%, the content of silicon is lowered by 50% or above, the grade of the calcium oxide is lowered to 1-2% from 3%, and the content of calcium is lowered by 50% or so.