The invention discloses a cable-less seabed observation system suitable for the whole sea depth, which comprises a water monitoring unit and a seabed observation platform. The seabed observation platform comprises a frame-type main body and a floating body, a wing plate, a floating ball cabin, a leveling mechanism, a counterweight and a release mechanism installed on the frame-type main body. Thefloating balloon cabin sealing system circuit is configured to deploy the wing plate when the seabed observation platform descends to a set height from the seabed, so that the seabed observation platform can land steadily. The leveling mechanism adjusts the seabed observation platform to stand horizontally on the seabed when the frame-type main body reaches the seabed. The release mechanism discards the counterweight to realize recovery after the underwater operation of the seabed observation platform is completed. The seabed observation platform of the invention adopts the cable-free laying mode, is not limited by the cable length, and the working water depth can reach 11,000 meters or more, so that the seabed observation of the whole sea depth can be realized.