In order to study the influence of rainfall on slope deformation and monitoring point arrangement, the finite difference-strength reduction method was used to calculate slope deformation under different reduction coefficients and rainfall intensity. The correlation degree between deformation of monitoring points and reduction coefficient can be obtained by using grey theory analysis, which can realize the optimization of slope deformation monitoring arrangement, and a monitoring point optimization arrangement plan was formulated according to an actual project. The results show that the slope is more possible to behave shallow failure due to rainfall. The application of grey relational degree in engineering can avoid the unnecessary monitoring points and make the monitoring data more conducive to guiding the warning work.