We present a study on 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). Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics, with the fourth and fifth being newly detected. Thirty-nine new times of maximum light are determined from the light curves, and combined with those in the literature, we construct the O - C diagram, derive a new ephemeris and determine a new value for the updated period of 0.104091579(2). In addition, the O - C diagram reveals an increasing rate of period change for 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 +/- 0.05 M-circle dot and age = (1.44 +/- 0.14) x 10(9) yr, respectively. With both the frequency of the fundamental radial mode and the rate of period change, YZ Boo is located at the post main sequence stage.