As a method to treat the magnesium surface for the bonded coupling of the mixture of the polymer and magnesium, this is a method comprising, (a) an etching step wherein the magnesium surface is treated by an acidic solution, (b) a first surface treatment step wherein the magnesium surface is treated by ultrasonic waves. (c) a second surface treatment step wherein the magnesium surface is treated by an acidic solution; (d) a first silane coupling processing step wherein the magnesium surface is treated by ultrasonic waves (e) a surface activation treatment step wherein the magnesium surface is treated by acidic solution (f) a second silane coupling processing step wherein the magnesium surface is treated by ultrasonic waves; and the step (a), is performed in an acidic solution mixing sulfuric acid, phosphoric acid and trace amounts of nitric acid, at 30~60°C for 10∼180 seconds. the step (b), proceeds by ultrasonic treatment with the alkali cleaning agent, at 30~60°C at 24~100 kHz and 400 W for 10~180 seconds. the step (c), proceeds a secondary etching with an acidic solution mixing sulfuric acid, phosphoric acid and trace amounts of nitric acid, at 30~60°C for 10~180 seconds. the step (d), proceeds with a mixed solution of 0.1∼20wt.% C 2 K 2 O 4, 0.1~10wt.% Na 2 O 3 Si, 0.01~1wt.% C 3 H 8 O 3 and 0.001-0.01wt.% C 20 H 24 Na 2 O 10 S 2 (sodium lignin sulphonate) adding 0.1~lwt.% Silane Coupling agent, at 30∼70°C, with 24~100kHz and 400 W for 10∼300 seconds. the step (e), proceeds with a mixed acidic solution of sulfuric acid and hydrochloric acid at a 30~70°C for 10∼300 seconds. the step (f), proceeds with a mixed solution of 0.1∼20wt.% C 2 K 2 O 4, 0.1~10wt.% Na 2 O 3 Si, 0.01~1wt.% C 3 H 8 O 3 and 0.001-0.01wt.% C 20 H 24 Na 2 O 10 S 2 (sodium lignin sulphonate) adding 0.1~lwt.% Silane Coupling agent, at 30∼70°C, with 24~100kHz and 400 W for 10∼300 seconds. (a) an etching step wherein the magnesium surface is treated by an acidic solution, (b) a first surface treatment step wherein the magnesium surface is treated by ultrasonic waves. (c) a second surface treatment step wherein the magnesium surface is treated by an acidic solution; (d) a first silane coupling processing step wherein the magnesium surface is treated by ultrasonic waves (e) a surface activation treatment step wherein the magnesium surface is treated by acidic solution (f) a second silane coupling processing step wherein the magnesium surface is treated by ultrasonic waves; and the step (a), is performed in an acidic solution mixing sulfuric acid, phosphoric acid and trace amounts of nitric acid, at 30~60°C for 10∼180 seconds. the step (b), proceeds by ultrasonic treatment with the alkali cleaning agent, at 30~60°C at 24~100 kHz and 400 W for 10~180 seconds. the step (c), proceeds a secondary etching with an acidic solution mixing sulfuric acid, phosphoric acid and trace amounts of nitric acid, at 30~60°C for 10~180 seconds. the step (d), proceeds with a mixed solution of 0.1∼20wt.% C 2 K 2 O 4, 0.1~10wt.% Na 2 O 3 Si, 0.01~1wt.% C 3 H 8 O 3 and 0.001-0.01wt.% C 20 H 24 Na 2 O 10 S 2 (sodium lignin sulphonate) adding 0.1~lwt.% Silane Coupling agent, at 30∼70°C, with 24~100kHz and 400 W for 10∼300 seconds. the step (e), proceeds with a mixed acidic solution of sulfuric acid and hydrochloric acid at a 30~70°C for 10∼300 seconds. the step (f), proceeds with a mixed solution of 0.1∼20wt.% C 2 K 2 O 4, 0.1~10wt.% Na 2 O 3 Si, 0.01~1wt.% C 3 H 8 O 3 and 0.001-0.01wt.% C 20 H 24 Na 2 O 10 S 2 (sodium lignin sulphonate) adding 0.1~lwt.% Silane Coupling agent, at 30∼70°C, with 24~100kHz and 400 W for 10∼300 seconds.