The constant rainfall is important for equatorial regions. The extreme rainfall shows our nature is facing climate change significantly and this needs to be paid attention by researchers hence the effects of disasters can be avoided as early as possible. Therefore, it is important to understand the rain pattern for the existing data so that forecasting can be done. This article discussed how to transform abnormal data into normal data and then analyze the data using the spline cubic analysis method. The study found that by using the transformation algorithm, the best r value is obtained. Cubic spline analysis shows that there are 30 rainfall stations in peninsular Malaysia where there are significant changes in rainfall patterns.