In order to predict and control the ink penetration depth, The base properties of 5 offset paper were firstly measured, namely, tightness、smoothness and K&N ink absorbency, etc. Then the penetration depth when offset magenta ink of the same volume entered into these papers was tested after printing. It was analyzed on the influences of offset paper and print processes on ink penetration depth. Finally, the relationships between the ink penetration depth under pressure and that under no pressure were studied. The results showed that both the tightness and smoothness of offset papers had impact on ink penetration into the paper internal structure, and the total ink penetration depth was about 1/5~1/3 of the thickness of the offset papers. In addition, the ink penetration depth under pressure was obviously lager than that under no pressure.