Abstract: The execution performance of a stack-based Java virtual machine (JVM) is limited by the true data dependency.To enhance the performance of the JVM, a stack operations folding mechanism for the picoJava-Ⅰ/Ⅱ processor was proposed by Sun Microsystems to fold 42.3% stack operations.By comparing the continuous bytecodes with predefined folding patterns in instruction decoder, the number of push/pop operations in between the operand stack and the local variable could be reduced.In this paper, a simple instruction folding algorithm is proposed for a Java processor.It is achieved on the FPGA, which greatly improve the performance of JVM.