Three miniature Joule-Thomson cryogenic coolers and a testing set up were built to investigate the cooling performance in this work. Shell-and-tube heat exchanger and plate fin heat exchangers with rectangular micro channels were designed to achieve high specific surface area. The main processing technology of micro mixed refrigerant cooler (MMRC) was described. The design and fabrication processing of the plate fin heat exchangers were also described. The new developed micro plate-fin type heat exchanger shows high compactness with the specific heat surface larger than 1.0x104 m<sup>2</sup>/m<sup>3</sup>. The results of experimental investigations on miniature mixed refrigerant J-T cryogenic coolers driven by a Mini-Compressor were discussed. The performance evaluation and comparison of the three coolers was made to find out the features for each type of cooler. Expressions of refrigeration coefficient and exergy efficiency were pointed out. No-load temperature of about 112 K, and the cooling power of 4.0W at 118K with the input power of 120W is achieved. The exergy efficiency of the SJTC is 5.14%.