The factors that restrict the isolation of an in-line dual stage optical isolator are analyzed using equivalent Jonse matrix. A new project for dual stage optical isolator is reported, which uses wedges of different angle for each stage. According to theoretical analysis, the isolation will be more than 58 dB. The result of volume production shows that the isolation of 80% products is more than 58 dB and the average isolation is 61 dB. So, this project can increase the isolation of a dual stage optical isolator largely.