This work discusses a two-step electroless plating method for preparing a Pt thin film on p-type InGaAs substrate, which is defined as Pt I and Pt II. A thin Pt catalytic layer formed in Pt I bath on the substrate at $65^{circ}C$. In the following Pt II bath, thick Pt films then easily grew on the sensitized layer on InGaAs previously formed in the Pt I bath. The growth of Pt film is strongly influenced by the plating temperature and pH value. To study the plating time effect, the plating of Pt II bath is 5 to 40 min at $80^{circ}C$ after using Pt I bath at 50~$65^{circ}C$ for 5min of pH 8~13. Pt film for ohmic contact to p-type InGaAs was successfully prepared by using the two-step Pt electroless plating.