In this paper, a hydroxyl-functional organophosphorus oligomer (HFPO) was introduced as a formaldehyde-free flame retardant into silk fabric, using 1, 2, 3, 4-butanetetracarboxylic acid (BTCA) as crosslinking agent. But HFPO bonded onto silk fabric is not theoretically increased with the increase of BTCA concentration. Triethanolamine (TEA) was applied to improve the HFPO fixation onto silk fabric. The paper still evaluated the flammability and physical properties of the silk fabric treated with HFPO/BTCA/TEA system. The treated silk fabric demonstrated a high level of flame retardancy with modest loss in fabric tensile strength. Microscale combustion calorimetry(MCC) testing results indicated that HFPO/BTCA/TEA system treated silk fabric has much lower heat release rate than that of control fabric.