The main similarity between the two is that they both were temples to the gods. The differences here is that Parthenon was made to celebrate Athena, the patron goddess of Athens, while the Pantheon was made to celebrate all the Roman gods and goddesses.
Another difference is the structure of the two temples. The Parthenon is a rectangular structure, while the main structure of the Pantheon is made to contain a sphere. The fronts of the two structures look very close, with space for sculptures