Both BaGa4Se7 (BGSe) and KTiAsO4 (KTA) can generate mid-infrared lasers pumped by 1.06 μm laser. Firstly, the phase matching curves of two kinds of non-linear crystals were simulated and calculated. The results show that BGSe with cutting angles of (56.3°, 0°) and KTA with cutting angle of (90°, 0°) can generate idle frequency light of ~3.5 micron under phase matching conditions of type I and type II-A, respectively. Then through theoretical calculation, the effective non-linear coefficients of BGSe (56.3°, 0°, type-I) is ?11.9 pm/V, and that of KTA (90°, 0°, type II-A) is ?3.2 pm/V. The OPO oscillation threshold of 15 mm long BGSe (56.3°, 0°, type-I) is 35.11% of that of 20 mm long KTA (90°, 0°, type II-A). Then, the experimental results show that the oscillation threshold of BGSe-OPO (56.3°, 0°, type-I, 15 mm) is smaller than that of KTA-OPO (90°, 0°, type-II-A, 20 mm). The output energy of BGSe (56.3°, 0°, type-I) is larger than that of KTA (90°, 0°, type II-A). Therefore, BGSe is a promising mid-infrared non-linear crystal.