Ptychography is a newly developed phase-retrieval technique based on lighting-probe scanning of a specimen in which the scanning step is smaller than the probe diameter. By using an iterative calculation, the complex-amplitude distributions of the probe and the specimen could be reconstructed simultaneously. Ptychography is a non-lens phase imaging technique with theoretically diffraction-limited resolution. Initially, the performance of Ptychography is limited by its basic assumptions. With the development of related researches in recent years, its characteristics have been gradually understood, and it has become increasingly mature as well. Nowadays, Ptychography has been applied to phase imaging, wavefront diagnostics, and optical metrology in the fields of visible, X-ray, and electrons. This paper discusses key factors that affect the reconstruction process and accuracy, including multiple modes, scanning errors, light-spot errors, distance errors, and non-negligible specimen thickness, and summarizes a development of key techniques to help overcome these factors.