This paper explores whether the spectral radiance of high-temperature targets in the shortwave infrared band (1300--2500 nm) has a directional effect and the relationship between the spectral radiance and the radiation zenith angle. Using 500 ℃ graphite and metal (304 stainless steel) plates as the high-temperature targets, this paper designs an experiment of spectral radiance measurement with 0°--70° radiation zenith angles of the high-temperature targets in a dark room. The variance analysis is applied to study whether the radiance in the shortwave infrared band gives a directional effect, and the least squares method is adopted to fit the directional spectral radiance of the high-temperature targets and thereby explore its variation rules. The experimental results show that under the condition of significance level α=0.01, the spectral radiance at different radiation zenith angles is significantly different for both the graphite plates and the metal plates. In light of the least squares method, the exponential function is used to fit the directional spectral radiance of the high-temperature targets, and the fitting accuracy is greater than 0.95. The results demonstrate that the metal plate has a more prominent directional effect than the graphite plate. The directional effect of the spectral radiance of the metal plate is affected by wavelength whereas that of graphite is not. The directional spectral radiance of both the two materials has an exponential relationship with the radiation zenith angle (0°--70°).