Four-way ball valve and hemodialysis device

The invention discloses a four-way ball valve which comprises a valve body, four through holes communicated with an inner cavity of the valve body are sequentially formed in the periphery of the valve body, the four through holes are a through hole A and a through hole B which are formed in a 180-degree opposite mode, and the four through holes are a through hole a and a through hole b which are formed in a 180-degree opposite mode; the ball core comprises an upper ball body and a lower ball body, the upper ball body is provided with three upper flow holes which are communicated with one another, the lower ball body is provided with three lower flow holes which are communicated with one another, and when the ball core is rotationally arranged in the inner cavity of the valve body, the three upper flow holes correspond to the through hole A, the through hole a and the through hole B respectively, and the three lower flow holes correspond to the through hole A, the through hole b and the through hole B respecti