The InAs thin films were grown on GaAs(100) substrate with $2^{circ}C$ tilted toward [$0ar{1}ar{1}$] with different As beam equivalent pressure (BEP) by using molecular beam epitaxy. Growth temperature and thickness of the InAs thin films were $480^{circ}C$ and 0.5 ${mu}m$, respectively. We studied the relation between the As BEP and the properties of InAs thin films. The properties of InAs thin films were observed by reflection high-energy electron diffraction (RHEED), optical microscope, and Hall effect. The growth, monitored by RHEED, was produced through an initial 2D (2-dimensional) nucleation mode which was followed by a period of 3D (3-dimensional) island growth mode. Then, the 2D growth recovered after a few minutes and the streak RHEED pattern remained clear till the end of growth. The crystal quality of InAs thin films is dependent strongly on the As BEP. When the As BEP is $3.6{ imes}10^{-6}$ Torr, the InAs thin film has a high electron mobility of 10,952 $cm^2/Vs$ at room temperature.