Downhole bypass valve while drilling

The invention relates to a downhole bypass valve while drilling. The downhole bypass valve comprises a downhole switching valve, an opened dart, a closed dark and a thrown dart receiving device. A valve element capable of sliding up and down and a spring which applies upward restoring force to the valve element are arranged inside the downhole switching valve. The opened dart is provided with an elastic stopping block which is opened outwards through pretightening force. The thrown dart receiving device is coaxially connected to the lower end of the downhole switching valve. In the normal drilling process, the bypass valve is in a closed state; when working is needed, the bypass valve can be opened or closed at any time under the ground. Different from an existing mode that ball throwing movement is adopted, the dart throwing mode is used for making opening and closing movement, and thus more reliability is achieved. Opening and closing can be conducted repeatedly under the ground without pulling out a drilling tool, and a large-particle leaking stoppage agent is used for leaking stoppage. Using is convenient, the drilling speed is high, fast leaking stoppage can be achieved, and efficient sand removing is realized.