Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions (RE3+) doped upconversion (UC) materials is still desirable. In this work, the intense single-band red emission is achieved by co-doping only Ho3+in the BiOCl:Er3+under 1550 nm excitation. In the BiOCl layered host, co-doping Ho3+ can further enhance the red emission and simultaneously suppress the green emission of Er3+, and thus obviously improve the red-to-green (R/G) ratio. It is found that Ho3+does not serve as energy trapping through the 5I6 state as in traditional UC materials but acts as ET bridge (4S3/2, 2H11/2 (Er3+) → 5F4, 5S2 (Ho3+) → 4F9/2 (Er3+)). The tuning mechanism of Ho3+ is discussed in detail and further confirms through a comparative experiment. Our research gives an unusual perspective to tune the UC behavior of Er3+ through co-doping Ho3+, which might be inspiring for achievement of single-band red UC emission.