Relating to an opioid receptor agonist (1S, 4S)-4-ethoxy-N-(2-((R)-9-(pyridin-2-yl)-6-oxaspiro[4.5]deca-9-yl)ethyl)-1, 2, 3, 4-tetrahydronaphthalen-1-amine fumarate salt, a fumarate salt crystal form I thereof, and a preparation method and an application therefor.