The invention discloses a platinum (II) coordination complex and a preparing method and application thereof. The preparing method includes the steps that active natural products such as oleanolic acid and ursodesoxycholic acid and derivatives of the active natural products serve as ligand; potassium tetrachloroplatinate(II) and ammonia or (R,R)-cyclohexanediamine are subjected to coordination reaction under the condition of potassium iodide, then iodide ions are removed through silver nitrate under the light shielding condition, and the mixture and sodium salt of ursodesoxycholic acid or oleanolic acid or the derivatives of oleanolic acid are reacted to obtain the product. The platinum (II) coordination complex has the good in-vitro antitumor activity, and can be applied to preparing medicine for treating malignant tumor.