Crosstalk and insertion loss are two important parameters for optical switching integrated chips. A new theoretical model of crosstalk in optical switching integrated chips, which is dependent on insertion loss and switch routing states, is put forward. As an example, the crosstalk and insertion loss coefficients of the optical switching integrated chip consisting of Mach-Zehnder interferometer (MZI)-based 4×4 Benes structure are measured by the 40 Gb/s differential quadrature phase shift keying (DQPSK) experiment under different switch routing states. The experimental results are consistent with the theoretical analysis. The crosstalk range for the16×16 Benes-type optical switching chips is calculated according to the given crosstalk and insertion loss coefficients.