We introduce the principles of conventional temperature measurement method and three-band infrared thermal imaging temperature measurement method for sea surface, then solve sea surface temperature with these two methods, separately, and comparatively analyze the measuring accuracies of the two methods under different observation directions and infrared imager precisions. The results show that three-band infrared thermal imaging temperature measurement method for sea surface can eliminate the influence of the sea surface emissivity error on the temperature measurement accuracy. When the infrared imager precision is within ±0.25 K, the deviation of sea surface measured temperature is less than 0.5 K, basically, so its accuracy is relatively high. Improving the infrared imager precision can effectively improve the accuracy of three-band infrared thermal imaging temperature measurement method for sea surface. When the zenith angle of observation direction is in the range from 70° to 85°, the deviation of conventional temperature measurement method is much larger than that of three-band infrared thermal imaging temperature measurement method for sea surface, so we must use three-band infrared imaging temperature measurement method for sea surface in this case.