It is significant to know the actual thermal gradients in sediments for complete understanding of occurrence of gas hydrates which are mostly affected by temperature and pressure regime. The thermal gradients in the gas hydrate drilling area of the South China Sea are almost obtained by needle temperature probes into the nearly seafloor sediments. But due to poorly consolidated condition and high permeability, the physical properties of seafloor sediments are more likely influenced by deep fluid drifting, thus rendering the extrapolations of some thermal gradients unreliable. Alternatively, in situ temperature measuring performed in the boreholes does obtain the actual thermal gradients of sediments, but with high cost and low efficiency that is often not affordable in the offshore drilling projects. To tackle the above problem, based on the previous computational model we utilize the single unsteady borehole temperature logging data and procedures to try to quickly reconstruct the actual thermal gradients. We also compare those reconstructed results with limited in situ thermal gradient measurements acquired by stationary temperature probes. The research shows that this method is valuable and practical when it applies to the section corresponding to smooth temperature variation such as in A-B interval. However, the modeled results are inaccurate in such uneven temperature variation as shown in B-C interval. We propose to be cautious with the method. The weights of other tedious factors that are omitted for the convenience can be increased when the environment of parameter system varies harshly, thus overwhelming the time-factor and reducing the rationality and reliability of the computation model.