Optical switch is a kind of important passive optical components in all-optical communication network. A kind of optical structure design method of 4×4 free-space optical switch is presented and a matrix theoretical analysis is made for this 4×4 optical switch structure. The 4×4 optical switch has a novel optical module configuration. It consists of polarization beam splitter, 1/4 wave plate, 1/2 wave plate, polarization optical modulator, right angle prism, and total reflection mirror. The operation is independent of the polarization states of input optical signals. Non-blocking optical switching can be implemented between input channels and output channels. This new kind of optical switch structure has the features of less optical components, compact size, modularity, polarization-independent. The routing control table for the 4×4 optical switch is given based on the matrix analysis. It provides a theoretical analysis method to describe routing controlling states between any one of the input channel and any one of the output channel of the 4×4 optical switch. So the routing controlling function of the non-blocked optical switching matrix can be realized expediently.