portion to a narrower lower portion on the other hand said second wrench body 2 comprises a perforation 23 with a stepped surface 231 between said second clamping piece 21 and said second handle piece 22 and said second wrench body 2 and therefore the perforation 23 directly face the tooth space 14 of said first wrench body 1 and also intersect with said first wrench body 1 on top of each other moreover a control component 3 is passed through said perforation 23 and said tooth space 14 in order to pin joint said first wrench body 1 and said second wrench body 2 among these a blocking piece 24 is positioned near said second clamping piece 21 of said second wrench body 2 and thus when said second wrench body 2 is opened with regard to said first wrench body 1 said blocking piece 24 is blocked by the side face 131 of the actuating piece 13 of said first wrench body 1 so that the opening up width of said second wrench body would be restricted as shown in fig6 the arc shaped structure of the side face 131 of the actuating piece 13 of said first wrench body 1 would increase the opening up width of said second wrench body 2 as compared to the long straight shaped prior art structure shown in fig1 and thereby increase the clamping diameter of the water pipe wrench and make it more convenient during use besides as shown in fig3 the present embodiment also comprises a bridge joint component.