The invention relates to a composite emulsifier suitable for oil base drilling fluid, a preparation method and applications thereof, and mainly aims to solve the problems that in the prior art, the variety of emulsifier for oil base drilling fluid is few, and the emulsifying performance and temperature resistant performance of conventional emulsifiers are bad. The provided composite emulsifier comprises the following components: (1) a main emulsifier, which is at least one of compounds represented by the structural formula (I); (2) an auxiliary emulsifier, which is at least one of alkyl phenolic ether carboxylate represented by the structural formula (II); and the ratio of auxiliary emulsifier to main emulsifier is in a range of 0 to 1 (included). The problems mentioned above are well solved. The emulsifier can be used as an oil base drilling fluid emulsifier, and has a good emulsifying performance and temperature resistant performance. The formed oil base drilling fluid has good stability and temperature resistant property, and can meet the special needs of drilling wells in a strong water sensitive and high temperature stratum, large displacement special drilling wells, and offshore horizontal wells.