Silicon-based optical switching delay line chip has a good application prospect in microwave photonic beamforming due to its simple structure and large instantaneous bandwidth. However, there are many difficulties in it's high-precision delay measurement, and the factors affecting the delay measurement stability are needed to be studied. By comparing the delay measurement stabilities of a delay test link based on optical vector network analyzing system, alignment waveguide and delay line, the main factors affecting the delay measurement stability of silicon-based optical switching delay line are analyzed experimentally. Experimental results show that chip insertion loss, input/output grating coupler package and residual Mach-Zehnder interference of delay line chip will deteriorate the on-chip delay measurement stability.