Abstract: Common departments of engineering survey depend on the solar ephemeris in the Chinese Astronomical Year Book for determining positions and directions by observing the Sun. This is extremely inconvenient. This paper, after analysing the calculations of the solar ephemeris according to the Newcomb's solar formula, establishes a simple mathematical model of solar ephemeris suitable for a pocket computer or programe calculator. Through the analysis of the accuracy of the calculation result based on this model, it concludes that the accuracy is high enough to make astronamical positions and orientations nowadays in generel engineering survey. Therefore the model will not only free engineering surveying from the Chinese Astronomical Year Book, but also increase the speed of its field work.