The dark current and relative spectral response of 4H-SiC ultraviolet p-i-n photodetector were investigated with the temperature decreasing from 300 K to 60 K by photocurrent measurement. It is found that the dark current and relative spectral response of the device declined during the whole period and that the higher the reverse bias voltage is, the faster the falling rate of dark current are. At the reverse bias of 0 V, when the temperature dropped, the peak response wavelength of the device firstly shifted slowly to the short wavelength direction and then moved to the opposite direction, reaching around 282 nm at 60 K. Meanwhile, a littie narrowing of relative spectral response of the device was observed. Furthermore, the mechanism of influences of temperature on photocurrent produced in p, i, n layers were investigated, and proposal lessening defect in i layer and reducing properly doping concentration in n layer were proposed to enhance the relative spectral response of the device.