The invention relates to drilling fluid for a low-pressure and water-sensitive stratum and a preparation method thereof, and mainly solves the problems that in the prior art, by emulsion droplets and organic soil particles in oil-based drilling fluid, non-conventional low pressure and low permeability, water sensitiveness and large water-phase activity difference are caused, a solid-phase damaged stratum is easily damaged, and tolerance of the oil-based drilling fluid to water invasion is poor. The drilling fluid comprises the following components in parts by weight: 100 parts of base oil, not less than 0.5 part of compound emulsifier comprising a main emulsifier and an auxiliary emulsifier which are shown in a formula (I), 0.1-5 parts of tackifier, 0.5-5 parts of filtrate reducer and 0-5 parts of alkaline substances. According to the technical scheme of the drilling fluid for the low-pressure and water-sensitive stratum and the preparation method, the problems are solved well. The drilling fluid can be used for a drilling and completion production technology for an oil and gas reservoir which has non-conventional low pressure and low permeability, water sensitiveness and large water-phase activity difference and easily causes the solid-phase damaged stratum.