Definition: The phenomenon of enlargement of the original enhancing lesion or the appearance of a new enhancing lesion soon after radiotherapy. Since this phenomenon is very similar to tumor recurrence, it is called pseudoprogression. Incidence: Pseudoprogression occurs in about 30-40% of patients after surgical resection of malignant glioma with radiotherapy and chemotherapy with temozolomide capsules. Problem: Once pseudoprogression occurs, because it is not easily distinguishable from tumor recurrence, it can greatly interfere with the treatment process and even lead to the emergence of wrong treatment. Solution: The most reliable method is to perform lesion biopsy through stereotactic technique and determine whether it is pseudo-progression or recurrence through pathological diagnosis? Clinical symptoms, MRI, PET/CT can provide reference. The following is a case of glioblastoma treated with radiotherapy and temozolomide chemotherapy after surgery. 7 months later, a new lesion appeared and a stereotactic biopsy was performed to confirm the pseudo-progression. Figure 1 The high signal (white) shown by red arrow in the MRI is the tumor Figure 2 The residual postoperative cavity shown by green arrow in the MRI and the newly appeared enhancing lesion shown by red arrow Figure 3 The gas at the lesion biopsy shown by green arrow in CT after stereotactic biopsy, indirectly confirming the accurate biopsy location