The work aims to prepare low-refractive index and low-loss large-core diameter optical fiber coating by performing screening test of photoinitiator. Thiol polydimethylsiloxane, vinyl silicone and photoinitiators were used to prepare polysiloxane UV-curing system functionalized by thiol-olefin. The effects of the system on refractive index, gel content, curing time and curing state were investigated. Then optimal photoinitiator was applied to field application test and fiber loss testing. In the five single-component photoinitiators, for coatings prepared by BP photoinitiation, the refractive index was 1.5795, optimal content 0.2% and fiber loss 7.1 dB/km; for coatings prepared by single-component Irgacure 184, the curing duration was 20 s, refractive index 1.5858, optimal content 1% and fiber loss 8.3 dB/km. In the four combined system, for coatings prepared by Irgacure1173+BP, the curing duration was 20 s, refractive index 1.5842, 1173: BP=2:1 and fiber loss 6.7 dB/km (the minimum). The addition of photoinitiator BP can reduce refractive index effectively in the polysiloxane UV-curing system functionalized by thiol-olefin. Coatings prepared by irgacure 184 are cured rapidly while coatings prepared by Irgacure1173+BP perform exhibits the lowest fiber loss.