Ink jet printing, as the key point of digital printing development, has already got some progress as technical be concerned, and also it has been used in industrial producing. But until now, ink jet printing still has some problems to be solved, include satellite droplet, droplet dimension, and spreading of droplet on substrate and so on. These problems involving parameters include dimension and geometry of the print-head, quality and characteristics of the control signal, surface tension of the ink, viscosity of the ink, characteristics of the substrate surface and so on. In this paper we just analysis the influence of ink surface tension to the process from jet to formation of the droplet by establishing mathematical model, but keep other parameters unchanged. At last, we get the relationship between ink surface tension and droplet parameters, so that it can be used as theoretical basement for print-head design and researching of ink.