We present a hybrid sort-first and sort-last parallel rendering system based on．retained-mode，called In-the-Core．which can render extreme large modeis on PC clusters．Traditional parallel systems have to issue all primitive-instructions when draw a new flame，or to copy whole scene on each node of cluster in advance．The approach can utilize full main memory capacity of cluster and lower the traffic of network．The main method is to partition a large model into smaller structures of elementary particle and distribmes them into the main memory of rendering nodes；meanwhile the load-balance is kept by view-depend partition algorithm with overhead feedback．Experiments on a cluster of 8 nodes show that the In-the-Core system can render models about 30～40M triangles at interactive frame-rate. It shows that a cluster of inexpensive PCs is all attractive alternative to those high-end graphics workstations.