Heterostyly, a genetically controlled floral polymorphism, includes both distyly and tristyly. In Boraginaceae, distyly was reported in several genera but it was rarely studied quantitively in the genus Arnebia. We experimentally studied the pollination ecology of Arnebia szechenyi, a perennial herb native to China. It exhibited precisely reciprocal herkogamy and marked between-morph pollen number and pollen shape dimorphism, and the ratio between the two morphs in each of the four populations studied was nearly equal to 1. This indicates an equilibrium ratio in distylous species with heteromorphyic self-incompatibility, which was further supported by the fact that no fruit was produced in flowers subjected to self-pollination or intra-morph pollination. In comparison with naturally pollinated flowers, hand inter-morph pollination increased both fruit set and seed set significantly, indicating pollen limitation in both morphs under natural conditions. Bombylius sp. and Nomia femoralis were the main visitors and could efficiently pollinate between the morphs of A. szechenyi. Overall, our results indicate that A. szechenyi is a typically distylous species with heteromorphic self-incompatibility, and the pollen limitation of seed production might suggest that distyly in A. szechenyi could be selected via male fitness.