During propagating through an underdense plasma, a laser will experience significant energy loss and will be trapped in the plasma as the frequency undergoing a redshift. Thus the electromagnetic (EM) soliton is formed. EM field distribution at different stage is constructed for the soliton in terms of primary theory and particle in cell (PIC) simulation. Radiography of solitons produced by laser accelerated MeV protons is investigated using Monte Carlo methods. The influencing fact or such as proton energy and source size is analyzed. Time-resolved radiography of the soliton is also carried out as the protons accelerated by the target normal sheath acceleration (TNSA) mechanism have a wide energy spectrum. Results validate the static electric field model of the soliton, and provide the basis for the future experiments.