A coupler for connection and assembly of an irrigation system is revealed. The coupler includes a base, a connecting portion and a retaining member. The base is for mounting the connecting portion and the retaining member. The connecting portion is arranged with a first channel and a second channel. The second channel is used to receive an insert that is connected to sprayers or hoses. The coupler features on that the second channel above the retaining member is arranged with a seal ring. While the insert is pressed downward axially, the insert is first against the seal ring so as to prevent water flow from being sprayed out of a gap of the second channel between an inner diameter of the connecting portion and an outer diameter of the insert.