The invention relates to a piston cylinder coaxiality detection device and method. The piston cylinder coaxiality detection device comprises a laser source (9), a two-dimensional position detector (11) and a controller (3), wherein the laser source (9) is used for transmitting a reference beam (8) overlapped with an axis of a cylinder tube (14) of a piston cylinder; the two-dimensional position detector (11) is installed on a piston (5) of the piston cylinder, and used for receiving the reference beam (8) and outputting the position at which the reference beam (8) irradiates on the piston (5);and the controller (3) is used for receiving the position information outputted by the two-dimensional position detector (11) and calculating the coaxiality of the piston (5) and the cylinder tube (14) according to the position information. The detection device in the embodiment of the invention detects the coaxiality of the piston and cylinder tube in the piston cylinder by using the laser source and the two-dimensional position detector, the structure is simple, and the cost is low; the detection device is convenient to adjust and suitable for being applied to the practical production site;and the detection device is high in coaxiality detection accuracy, and has a good guiding significance for the assembling quality of the piston and cylinder tube in the piston cylinder.