With the rapid increase of patents, patent clusters formed by a large number of patents are becoming a new phenomenon in the patent field. Patent clusters are also referred to as patent thickets, because they are similar to lush thickets. It has become an urgent task to measure patent thickets and analyze the evolution from the massive data. The generation mechanism of patent thickets has been analyzed in this paper. The measurement index of the patent thicket is developed based on valid patents. The hierarchical cluster analysis is employed to classify the evolution periods of patent thickets. Taking inkjet printing technology as the research sample, the methods are employed to measure the patent thickets and analyze the evolution with the data of long-term time series.