The invention provides a method for exploiting a high-inclined-angle heavy oil reservoir by plane gravity displacement. According to the method for exploiting the high-inclined-angle heavy oil reservoir by plane gravity displacement, a plane gravity oil displacement mode using steam injection as a major measure and non-condensable gas injection as an auxiliary measure is designed. Steam and non-condensable gas are proportionally injected; high-temperature hot water and non-condensable gas in the stratum can easily form a secondary gas cap and a secondary water zone with the obvious spatial variation effects due to the density differences; the high-temperature secondary water zone provides a heating resource for a downstream cold oil zone; and the breakthrough of the injection gas towards a production well in a low structure position is prevented. Meanwhile, the oil reservoir integral scaled development is realized; the unidirectional linear staggered well network development is used; and the plane conformance coefficient and the recovery efficiency are improved.