<p>In recent years, gradient hydrogels have aroused great interest because of their heterogeneous structure and irregular shape changes. The gradient hydrogels have been widely used in tissue engineering and biomedical fields, because they can respond to stimuli to achieve functions. In general, gradient hydrogels are prepared by applying an external field. The applicable conditions of various external fields are different, and the appropriate preparation method should be selected according to the needs. In this mini-review, we classified and discussed the external fields that induce gradient structure of hydrogel, such as gravitational field, temperature field, light field, electric field, magnetic field, and acoustic field. We hope that this article can provide new insights for the design of gradient hydrogels.</p> Graphical Abstract <p>We classified and discussed the external fields that induce gradient structure of hydrogel, such as gravitational field, temperature field, light field, electric field, magnetic field and acoustic field. We also look at their challenges and development prospects </p>