Disclosed are a platinum (II) compound, a preparation method therefor, and a pharmaceutical composition and an application thereof. The preparation method comprises the following steps: enabling dihydrate diammine platinum nitrate (4) to react with the carboxylate ligand derivative (5) in water, to produce a platinum (II) compound. Also provided are an application of the platinum (II) compound in preparation of an antitumor drug, and a pharmaceutical composition. The pharmaceutical composition contains an active component and a medicinal carrier, the active component containing the platinum (II) compound, and the mass percentage of the active component being 0.1%-95%. The platinum (II) compound of the present invention is well water-soluble, low toxic, easily prepared, and efficient in antitumor activity.
