The invention discloses a preparation method of a novel polyester fiber and particularly relates to the preparation method of a high-comfort triangular hollow microporous fiber which is newly developed and has the advantages of being dry, comfortable, cool and refreshing, capable of absorbing sweat and draining moisture, light, good in warm keeping, easy to clean, fast to dry and the like. According to the preparation method of the high-comfort triangular hollow microporous fiber, the online measurement addition technique and a melt spinning process are adopted, three symmetrical V-shaped spinneret plates serve as spinneret assemblies to obtain the fiber, and an alkali reduction process is performed to obtain the high-comfort triangular hollow microporous fiber. The fiber fabric has the advantages of being dry, comfortable, cool and refreshing, capable of absorbing sweat and draining moisture, easy to clean, fast to dry, light, good in warm keeping and the like.