  In this paper, we present the first light curve synthesis and orbital period
change analysis of nine contact binaries around the short period limit. It is
found that all these systems are W-subtype contact binaries. One of them is a
medium contact system while the others are shallow contact ones. Four of them
manifest obvious O'Connell effect explained by a dark spot or hot spot on one
of the component stars. Third light was detected in three systems. By
investigating orbital period variations, we found that four of the targets
display a secular period decrease while the others exhibit a long-term period
increase. The secular period decrease is more likely caused by angular momentum
loss while the long-term period increase is due to mass transfer from the less
massive component to the more massive one. Based on the statistic of 19
ultrashort period contact binaries with known orbital period changes, we found
that seven of them display long-term decrease (three of them also exhibit
cyclic variations), ten of them manifest long-term increase while two of them
only show cyclic variation and that most of them are shallow contact binaries
supporting the long timescale angular momentum loss theory suggested by
Stepien. For the three deep contact systems, we found that they are probably
triple systems. The tertiary companion plays an essential role during their
formation and evolution.
