The invention relates to a low-density foam workover fluid for a deep-layer low-pressure oil and gas well and a preparation method of the low-density foam workover fluid. The low-density foam workover fluid comprises the following components in percentage by mass: 0.40-0.50% of a foaming agent, 0.45-0.55% of a foaming agent aid, 0.60-0.80% of a foam stabilizer, 0.20-0.25% of an auxiliary foam stabilizer and the balance of fresh water. The low-density foam workover fluid has the temperature resistance of 150 DEG C, the NaCl resistance of 20%, the CaCl2 resistance of 15% and the crude oil pollution resistance of 15% and can meet the requirement for workover construction of deep wells and ultra-deep wells under the rigorous conditions of high temperature, high salinity and the like; and the density of the workover fluid can be regulated between 0.35g/cm<3> and 0.85g/cm<3> according to the field process requirement, the maximum filter loss of the workover fluid API is only 9.6mL, and the filter loss is relatively small, so that the low-density foam workover fluid can be used for operation of low-pressure wells and high-loss wells. The low-density foam workover fluid is simple in preparation process and has favorable application prospects in workover operation of low-pressure deep wells and ultra-deep wells.