The present disclosure is related to systems and methods for determining a field map in magnetic resonance imaging (MRI). The method includes obtaining at least three images. Each may be acquired at one of at least three echo times by an MRI device via scanning a subject. The at least three echo times may define multiple pairs of adjacent echo times. Each of the multiple pairs of adjacent echo times may have a time difference between the adjacent echo times. At least two of the time differences may be different. The method includes determining a target function with an off-resonance frequency as an independent variable. The target function includes a phase deviation term and a sparsity constraint term.