The invention provides an emulsifier for oil-base mud and a preparation method of the emulsifier. The emulsifier for oil-base mud comprises the following components in percentage by weight: 10-50% of oleyl alcohol, 10-50% of a compound A, 5-30% of a compound B, 5-40% of a compound C, 5-40% of a compound D, 5-40% of a compound E, 5-40% of a compound F, 1-10% of glycerin and less than 5% of fatty oil, totaling 100%. The invention further provides a method for preparing the emulsifier for oil-base mud. The emulsifier for oil-base mud disclosed by the invention can be used for high-temperature high-density oil-base mud.