The theoretical analysis for the focusing properties of spiral zone plate is presented. Using the diffraction theory, focusing properties of spiral zone plate and the series-form expression for the diffracted field near the hollow focus are calculated. Moreover numerical simulation and theoretical analysis for the imaging are also carried out by a spiral zone plate using our theoretical results. It shows that the spatial resolution of a spiral zone plate is associated with the zone width of its hollow focus. Experimental results indicate our theoretical analyses are consistent with the experimental test, which give out an effective method for the imaging analysis and numerical simulation of spiral zone plate.