Zoom lens system

The present invention provides a zoom lens system. The zoom lens system comprises a first lens assembly with a positive refractive power, a second lens assembly with a negative refractive power, a third lens assembly with a positive refractive power and a fourth lens assembly with a positive refractive power. The first lens assembly to the fourth lens assembly are arranged in turn from an object side to an image side. Zooming is executed through changing distance among the first lens assembly to the fourth lens assembly. In the zooming period, the first lens assembly and the third lens assembly are fixed in relative to an image plane while the second lens assembly and the fourth lens assembly move. At least one lens assembly of the first to fourth lens assemblies comprises at least one aspheric surfaces, and at least one lens assembly of the first to fourth lens assemblies comprises a balsaming lens.