A novel interferometric fiber sensor based on different multimode core diameters of optical fiber cascade is proposed.The core diameter of the multimode optical fiber (MMF1) is 50μm,on its left side,a large core multimode fiber (MMF2) with the cladding re moved is welded,and its core diamet er is 105μm,constructing the sensing region.In the experiment,the cladding of MMF2is removed by the hydrof luoric acid (HF).Due to the fiber core mismatch,both of multimode fibers will produce a variety of core modes,mutual interference will happen among them,and then there will be a series of interference dips wi th different sensitive characteristics. This paper uses these interference dips with different sensitivities to tempera ture and liquid level to realize the simultaneous measurement of them.The experimental results show that the temperature sensitivities of the three interference dips are 0.066nm/℃, 0.139nm/℃and 0.031nm/℃,respectively. We take the levels of sensitivities to water and salt water of the three dips f or experiment comparison,and the level of one of the three dips sensitivities is up to －1.251nm/mm.The experiment pro ves that this sensor system is low cost,simple structure,so it can be used for temperature and liquid level measure ment at the same time,in oil production,biological and pharmaceutical etc,it has potential application value.