Pre soaked super absorbent polymer(SAP) was incorporated into high strength concrete(HSC) as internal curing agent to study its effects on early age shrinkage and mechanical properties. The amount of additional water introduced by SAP was fixed at 5% and 10% of the mass of cement respectively. Results show that pre soaked SAP significantly decreases autogenous shrinkage(AS) and early age drying shrinkage(DS) of HSC. The main mechanism is that the pre soaked SAP effectively reduces the driving force of AS and DS by heightening the inner relative humidity(RH) in concrete via releasing water when inner RH drops. The shrinkage reducing ratio can reach above 90% for AS and up to 75% for total shrinkage under dry condition. Nevertheless, addition of SAP has an unfavorable effect on strength development of HSC to some extent and late strength is less affected by addition of SAP. When the amount of additional water introduced by SAP is 5% of the mass of cement, the compressive strength at 28d reaches 95% of the control HSC. Thus, it would not impede engineering application of SAP in HSC. In addition, compared with simply increasing the water cement ratio, the effectiveness of pre soaked SAP in shrinkage reduction of HSC is much more pronounced and the harmful effect on strength is obviously less.