We present a large scale map of about 15′ × 15′ of CO(J=1−0) toward W51 giant molecular cloud (GMC), which covers the most active star-forming region of W51 GMC, and an interferometry HCO+(J=1−0) map of a high spatial resolution (i.e. 8″ × 6″.1) with a field of view (2′ × 2′) centered at W51IRS1. A structure model of W51GMC is obtained according to the results of the observations and analyses. The observations demonstrate that some small molecular cores generated by the collision between the W51GMC and the 60–73 km·s-1 foreground cloud are collapsing toward their own centers. In addition, 16 new molecular cores are discovered from the HCO+(J=1−0) map.