Hi Hitesh,
SAP PS is used to map the project management and logistics areas of a company. It allows the users to create Projects, Monitor timelines, budget the project, assign resources etc. To get more on PS check
Project System (PS) - SAP Library
Whereas the SAP PMS is used to monitor the performance of the SAP system installed. You can get more details on SAP PMS from below link
http://www.is4it.de/fileadmin/images/pdf/pdf-en/IS4IT_PMS_A4_engl_email.pdf
Hope it helps..
Regards
Sammar