  We present a study on the pulsations of the high-amplitude $\delta$ Scuti
star YZ Boo based on photometric observations in Johnson $V$ and $R$ bands with
both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory (XAO) and
the Xinglong 85-cm telescope of National Astronomical Observatories, Chinese
Academy of Sciences (NAOC). The Fourier analysis of the light curves reveals
the fundamental radial mode and its five harmonics, with the fourth and the
fifth newly detected. 39 new times of light maximum are determined from the
light curves, and combined with those in the literature, we construct the $O -
C$ diagram and derive a new ephemeris and the determination of a new value of
the updated period 0.104091579(2). Besides, the $O - C$ diagram reveals an
increasing period change rate of YZ Boo. Theoretical models are calculated and
constrained with the observationally determined parameters of YZ Boo. The mass
and age of YZ Boo are hence derived as $M$ = 1.61 $\pm$ 0.05 $M_\odot$ and
$age$ = (1.44 $\pm$ 0.14) $\times$ 10$^9$ yr, respectively. With both the
frequency of the fundamental radial mode and the period change rate, YZ Boo is
located at the post-main-sequence stage.
