Interferometric Particle Imaging (IPI) technique is presently utilized in measuring irregular particle whose shape and size are indispensable parameters in various scientific fields, while orientation and size uncertainty are tough problems in IPI measurement. Herein, an effective method is proposed to eliminate aforementioned uncertainties. Based on Square Gradient function and multi-plane phase retrieval algorithm, our method eliminates conjugate solution in single-plane shape reconstruction thereby making the orientation of the reconstructed particle shape unique, while position search of focused image has significantly reduced the size error of reconstructed particle shape. Dual-detector IPI system is constructed to measure actual irregular particles whose shapes are successfully recovered from detected defocused speckles with an average shape similarity of 0.960 in Jaccard Index, and theoretical size error greatly decreases from 44.7% to 0.8% under the same system configuration. The proposed method is potential in further work such as real-time particle measurement and 3D shape reconstruction.