A pharmaceutical composition used to treat Parkinson's disease contains levodopa, carbidopa and entacapone or pharmaceutically acceptable salt thereof, and at least one kind of pharmaceutically acceptable excipients. Entacapone is not mixed with levodopa or carbidopa in the pharmaceutical composition. The preparation method of the pharmaceutical composition includes making the first particles with levodopa and carbidopa, making the second particles with entacapone, and then pressing the two kinds of particles into tablets.