Visible IR-to-green photon-avalanche upconversion is reported in an ${\mathrm{Ho}}^{3+}$ singly doped $\beta -\mathrm{Na}\left(Y_{1.5}{\mathrm{Na}}_{0.5}\right)F_6$ crystal under $980\mathrm{nm}$ excitation. Upconverted green, red, and IR emissions are observed at 540, 645, and $751\mathrm{nm}$ , respectively. Temporal evolution and excitation power dependent upconversion intensity are measured, suggesting that a photon-avalanche mechanism is responsible for the upconversion process. It is believed that an efficient cross relaxation $({}^{5}S_2,{}^{5}I_8)\to ({}^{5}I_6,{}^{5}I_6)$ mainly performs the population of ${}^{5}I_6$ excited state, resulting in the intense photon-avalanche upconversion emission in the synthesized samples.