  We here report the photometric performance of Lunar-based Ultraviolet
telescope (LUT), the first robotic telescope working on the Moon, for its
18-months operation. In total, 17 IUE standards have been observed in 51 runs
until June 2015, which returns a highly stable photometric performance during
the past 18 months (i.e., no evolution of photometric performance with time).
The magnitude zero point is determined to be $17.53\pm0.05$ mag, which is not
only highly consistent with the results based on its first 6-months operation,
but also independent on the spectral type of the standard from which the
magnitude zero point is determined. The implications of this stable performance
is discussed, and is useful for next generation lunar-based astronomical
observations.
