The earliest known translation of Indian Buddhist scriptures into Chinese was in 148 CE.
At this time, a people known as the Kushans from Central Asia were ruling the land between China and India.
Their kingdom was centered on a region known as Gandhara in modern-day Pakistan and Afghanistan.
The Kushan rulers patronized an early form of Mahayana Buddhism, which was particularly popular in Gandhara then.
Since the Kushans favored Mahayana doctrine, and they controlled the path between India and China, this was the primary form of Buddhism that was brought in that direction to China.