The laue bent crystal is the most effective optical element of focusing, collimating and monochromating of high flux density hard X-rays (above 30 keV) from the insertion device radiation, because of reducing the high heat load effectively. So the study of the focusing optical properties is important for developing high performance and stability laue bent crystal monochromator. We give a systematic research of the focusing properties of laue bent crystal by X-ray trace program self-developed, analyze the effects of the mode of incident beam and crystal parameter on focusing spot size, focal length, diffracted beam divergence, etc., and obtain the following results: the higher the diffracted energy, the smaller the spot size is and the spot size tends to be a constant; the smaller the bend radius of crystal, the smaller the spot size is, and the spot size reaches a minimum when the bend radius is a threshold, then as the bend radius decreases, the spot size becomes larger because of aberration; the spot size is linearly directly proportional to the thickness of crystal. For the divergence of diffracted beam, it becomes smaller as the diffracted energy is high, and tends to be a constant; it is linearly directly proportional to the curvature of bent crystal. Also we obtain a reasonable range of bent crystal parameters from the study by ray-tracing.