The invention belongs to the technical field of geophysical exploration and relates to an ocean controllable source electromagnetic response calculating method. The method is characterized in that a GPS/depth sensor mounted on a launcher is used to measure the position deviation of the launcher and a preset measuring line, substituting the position deviation data into a geological calculation model, allowing an electric dipole to be equivalent to a finite line source and performing subsection calculation, breaking up a sectioned long straight wire of optional morphology into horizontal and vertical equivalent electric dipoles under an observation coordinate system, respectively calculating the electromagnetic response of each section, using an analytic formula to solve an ambient field, using a staggered finite volume method to solve an induction field, and superimposing vector fields to obtain sectioned wires and the ocean controllable source electromagnetic response based on the actually-measured launcher morphology data. The method has the advantages that launcher morphology parameters can be monitored precisely, the method can approach the actual operation working conditions to the maximum extent, and the accuracy of electromagnetic response calculation and inversion can be increased effectively by using a finite line source treatment method.