Considering characteristics of beam output from output single emitter diode laser, beam width is described using 1/e2 maximum, power in bucket and second moment. The beam parameter product (BPP) in various definitions based on the hyperbolic fitting method with approximation of Gaussian beam can be obtained. The calculated BPPs of the beam from a single emitter diode laser are compared with the BPP of fiber with core diameter of 105 μm and numerical aperture of 0.2. The side mode increases gradually with increasing injection current, leading to deterioration of the beam quality, and reduces the coupling efficiency. As the injection current increases from 1 A to 13 A, the coupling efficiency decreases from 96.5% to 88.8% . Therefore, the beam width defined by the second moment is an accurate method for the description and evaluation the beam quality of single emitter diode laser based on BPP.