Caffeine is an FDA-approved drug for preventing and treating apnea in preterm infants. However, the pharmacokinetic (PK) characteristics of caffeine in preterm infants differ significantly from those in adults. Several population pharmacokinetic (PopPK) models have been developed to investigate potential covariates influencing PK parameters. This review aimed to summarize PopPK studies of caffeine in preterm infants and explore the identified influencing covariates. It has been observed that most caffeine pharmacokinetics followed a one-compartment model (1-CMT), although one study utilized a three-compartment model (3-CMT). Various covariates including birth weight, current weight, genetic polymorphism, combination medications, feeding patterns, and pathological conditions have been identified to affect caffeine PK parameters in preterm infants. Developing an individualized dosing regimen for preterm infants is essential for safe and effective treatment. Future PopPK studies of caffeine in preterm infants should focus on sampling and feeding patterns and further explore the effects of other covariates like gestational and postnatal age on caffeine PK parameters, which should be taken into account in the individualized dosing regimen of caffeine.