The present invention relates to the 3D seismic marine survey, more particularly, relates to a foldable-fixing type 3D seismic survey apparatus for a small ship and a method of 3D seismic survey by using the foldable-fixing type 3D seismic survey apparatus which enalbe the relative position of a detector to be fixed and adopt a foldable structure to be convenient for the conveying, installation and the 3D seismic marine survey. The foldable-fixing type 3D seismic survey apparatus for the small ship includes: a seismic wave generator; the detector comprising a plurality of floating board units; and foldable fixing-frames connecting and fixing the floating board units to each other in a floating board array such that relative positions of the floating board units are fixed, and being folded for transporting and unfolded for installing. After moving to the detection position and the above detector is unfolded and installed, the seismic unit receives 3D seismic waves while being towed behind the seismic wave generator.