In Thailand, the major cause of heat sealing problem is that temperature at the interface surface of material is not monitored and controlled appropriately. Conventional testing method of seal strength ASTM F88-07 and JIS Z0238 are extensively used in industries and researches. Conventional method use wide temperature pitch for heat sealing. The variation of heat seal strength of conventional method is very high because to temperature traceability use only display from heat sealing machine. With the innovative method, temperature of melting surface is monitored and controlled directly. In this study, the step of heating temperature for heat seal strength testing is 1-2°C for obtaining details of heat seal strength. Temperature measurement and display were calibrated before applying heat sealing process. The differences from the convention method and proposed method are discussed. The objectives of this research are as follows. Firstly, investigation of trouble section in conventional testing method. Secondly, the new test method for high accuracy of heat seal sample. Experiments are conducted to prove the superiority of new proposed method.