The invention relates to the technical field of piston type compressor assembling parts, in particular to a stable connection device with a built-in elastic locking block for a piston type compressor.The stable connection device comprises a crosshead body, a crosshead nut fixed to the upper end of the crosshead body and a piston rod fixed to the crosshead nut. According to the stable connection device with the built-in elastic locking block for the piston type compressor, since a right-angle steel plate with an up-down connection through hole is fixed to the upper end of the crosshead body through a bolt, a fastening steel block with the built-in elastic locking block is inserted into the right-angle steel plate, a fixing bolt inside the fastening steel block is used for being crewed intoan internal thread adjusting hole to fix and adjust the position of the locking block, the problem that piston rods of small and medium compressors are likely to be loosened under the conditions thatreciprocating inertial force is large, working time is long and the working intensity is large is avoided, and compressor continuous working safety and reliability are effectively improved.