A hydraulic oil metal particle detection sensor based on the dualsolenoid coil with casing structure is proposed. Theoretical analysis shows that the casing structure sensor can couple the magnetic field intensity of external solenoid coil and utilize the mutual inductance between double solenoid coils. In this way, the inductance variation of metal particles through the detection area is increased effectively. Inductance variation, average noise, and signaltonoise ratio are selected as metrics for measuring the detection sensitivity. Comparative experiments show that the casing structure sensor not only does not increase detection noise, but also is superior to single solenoid structure sensor in terms of inductance variation and signaltonoise ratio for the detection of same metal particles. With the increase of iron particle size, the superiority of detection ability is more obvious. When it detects iron particles and copper particles ranging from 110 to 120 μm, the inductance variation increases by 24 times and 17 times respectively. Compared with those of single solenoid structure sensor, the signaltonoise ratio increases by 18 times. The lower limit of particle detection experiments show that the casing structure sensor can detect iron particles with diameter larger than 30 μm and copper particles with diameter larger than 90 μm. The research has reference significance for improving the detection sensitivity of solenoid inductance sensor.