An alkali metal ion modified titanium silicalite zeolite for gas phase epoxidation of propylene and hydrogen peroxide and a preparation method thereof. The method includes, at first step: preparing an alkali metal hydroxide modification solution; at second step: conducting controlled hydrothermal treatment on a TS-1 zeolite matrix by using an alkali metal hydroxide solution; and at third step: conducting post-treatment on the hydrothermally modified TS-1 zeolite, including solid-liquid separation, washing, drying and calcining. In the washing process, the modified TS-1 zeolite wet material is washed with a low concentration alkali metal hydroxide solution; alkali metal ions are reserved on the silicon hydroxyl of the modified titanium silicalite zeolite; and an infrared characteristic absorption band of a framework titanium active center modified by the alkali metal ions is in a range above 960 cm−1 and below 980 cm−1.