This paper puts forward an improved fast-LADT arithmetic in application of electrocardiogram(ECG) compression.The arithmetic has much less mathematical operation and much easier to be implemented in hardware.With the artificial and experimental verification,it turns to be that the arithmetic keeps rather high compress ratio,has the advantages of small distortion and has the nicer results in real tine.The hardware system of ECG data compression is designed,implements the improved fast-LADT arithmetic,the experiment of ECG data compression also has been carried out,and the experiment results prove the validity of the arithmetic.